I found the following gems is causing the error
$ cat Gemfile
gem 'fancy-buttons', :git =>'git://github.com/imathis/fancy-buttons.git'
$ jruby-1.6.1/bin/jruby -v
jruby 1.6.1 (ruby-1.9.2-p136) (2011-05-07 3fe11da) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_24) [linux-amd64-java]
$ jruby-1.6.1/bin/jruby -S bundle install
Updating git://github.com/imathis/fancy-buttons.git
RubyException$i$0$2$initialize.gen:65535:in `call': java.lang.ClassCastException: org.jruby.RubyObject cannot be cast to org.jruby.RubyException
from CachingCallSite.java:242:in `cacheAndCall'
from CachingCallSite.java:80:in `callBlock'
from CachingCallSite.java:84:in `call'
from RubyClass.java:820:in `newInstance'
from RubyException.java:211:in `exception'
from RubyException$s$0$1$exception.gen:65535:in `call'
from DynamicMethod.java:213:in `call'
from DynamicMethod.java:209:in `call'
from RubyClass.java:685:in `finvoke'
from RuntimeHelpers.java:548:in `invoke'
from RubyBasicObject.java:358:in `callMethod'
from RubyKernel.java:1009:in `convertToException'
from RubyKernel.java:987:in `raise'
from PsychParser.java:242:in `parse'
from PsychParser$i$1$0$parse.gen:65535:in `call'
from CachingCallSite.java:137:in `call'
from CallOneArgNode.java:57:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:190:in `call'
from DefaultMethod.java:179:in `call'
from CachingCallSite.java:137:in `call'
from FCallOneArgNode.java:36:in `interpret'
from CallNoArgNode.java:62:in `interpret'
from LocalAsgnNode.java:123:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:190:in `call'
from DefaultMethod.java:179:in `call'
from CachingCallSite.java:137:in `call'
from FCallOneArgNode.java:36:in `interpret'
from LocalAsgnNode.java:123:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:190:in `call'
from DefaultMethod.java:179:in `call'
from CachingCallSite.java:282:in `cacheAndCall'
from CachingCallSite.java:139:in `call'
from CallOneArgNode.java:57:in `interpret'
from LocalAsgnNode.java:123:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:190:in `call'
from DefaultMethod.java:179:in `call'
from CachingCallSite.java:282:in `cacheAndCall'
from CachingCallSite.java:139:in `call'
from CallOneArgNode.java:57:in `interpret'
from NewlineNode.java:103:in `interpret'
from RescueNode.java:216:in `executeBody'
from RescueNode.java:120:in `interpretWithJavaExceptions'
from RescueNode.java:110:in `interpret'
from BeginNode.java:83:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:111:in `INTERPRET_BLOCK'
from Interpreted19Block.java:203:in `evalBlockBody'
from Interpreted19Block.java:154:in `yield'
from Block.java:130:in `yield'
from RubyDir.java:335:in `chdir'
from RubyDir$s$0$1$chdir.gen:65535:in `call'
from DynamicMethod.java:213:in `call'
from CachingCallSite.java:292:in `cacheAndCall'
from CachingCallSite.java:148:in `callBlock'
from CachingCallSite.java:157:in `callIter'
from CallOneArgBlockNode.java:60:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:190:in `call'
from DefaultMethod.java:179:in `call'
from CachingCallSite.java:282:in `cacheAndCall'
from CachingCallSite.java:139:in `call'
from CallOneArgNode.java:57:in `interpret'
from DAsgnNode.java:110:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:111:in `INTERPRET_BLOCK'
from Interpreted19Block.java:203:in `evalBlockBody'
from Interpreted19Block.java:154:in `yield'
from Block.java:130:in `yield'
from RubyArray.java:1595:in `eachCommon'
from RubyArray.java:1602:in `each'
from RubyArray$i$0$0$each.gen:65535:in `call'
from CachingCallSite.java:272:in `cacheAndCall'
from CachingCallSite.java:114:in `callBlock'
from CachingCallSite.java:123:in `callIter'
from CallNoArgBlockNode.java:64:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from IfNode.java:117:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:120:in `call'
from DefaultMethod.java:145:in `call'
from SuperCallSite.java:68:in `callBlock'
from SuperCallSite.java:75:in `call'
from ZSuperNode.java:100:in `interpret'
from NewlineNode.java:103:in `interpret'
from RescueNode.java:216:in `executeBody'
from RescueNode.java:120:in `interpretWithJavaExceptions'
from RescueNode.java:110:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:147:in `call'
from DefaultMethod.java:163:in `call'
from CachingCallSite.java:103:in `call'
from VCallNode.java:85:in `interpret'
from InstAsgnNode.java:95:in `interpret'
from OpAsgnOrNode.java:99:in `interpret'
from NewlineNode.java:103:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:147:in `call'
from DefaultMethod.java:163:in `call'
from CachingCallSite.java:103:in `call'
from VCallNode.java:85:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:147:in `call'
from DefaultMethod.java:163:in `call'
from CachingCallSite.java:103:in `call'
from CallNoArgNode.java:62:in `interpret'
from CallNoArgBlockNode.java:60:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from IfNode.java:117:in `interpret'
from IfNode.java:119:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:111:in `INTERPRET_BLOCK'
from Interpreted19Block.java:203:in `evalBlockBody'
from Interpreted19Block.java:154:in `yield'
from Block.java:130:in `yield'
from RubyArray.java:1595:in `eachCommon'
from RubyArray.java:1602:in `each'
from RubyArray$i$0$0$each.gen:65535:in `call'
from CachingCallSite.java:112:in `callBlock'
from CachingCallSite.java:123:in `callIter'
from CallNoArgBlockNode.java:64:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:147:in `call'
from DefaultMethod.java:163:in `call'
from CachingCallSite.java:103:in `call'
from VCallNode.java:85:in `interpret'
from LocalAsgnNode.java:123:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from IfNode.java:119:in `interpret'
from NewlineNode.java:103:in `interpret'
from BeginNode.java:83:in `interpret'
from InstAsgnNode.java:95:in `interpret'
from OpAsgnOrNode.java:99:in `interpret'
from NewlineNode.java:103:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:147:in `call'
from DefaultMethod.java:163:in `call'
from CachingCallSite.java:262:in `cacheAndCall'
from CachingCallSite.java:105:in `call'
from VCallNode.java:85:in `interpret'
from CallOneArgNode.java:57:in `interpret'
from LocalAsgnNode.java:123:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from BeginNode.java:83:in `interpret'
from InstAsgnNode.java:95:in `interpret'
from OpAsgnOrNode.java:99:in `interpret'
from NewlineNode.java:103:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:147:in `call'
from DefaultMethod.java:163:in `call'
from CachingCallSite.java:262:in `cacheAndCall'
from CachingCallSite.java:105:in `call'
from VCallNode.java:85:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:147:in `call'
from DefaultMethod.java:163:in `call'
from CachingCallSite.java:262:in `cacheAndCall'
from CachingCallSite.java:105:in `call'
from CallNoArgNode.java:62:in `interpret'
from IfNode.java:119:in `interpret'
from NewlineNode.java:103:in `interpret'
from IfNode.java:119:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:190:in `call'
from DefaultMethod.java:179:in `call'
from CachingCallSite.java:282:in `cacheAndCall'
from CachingCallSite.java:139:in `call'
from CallOneArgNode.java:57:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:276:in `call'
from DefaultMethod.java:211:in `call'
from CachingCallSite.java:322:in `cacheAndCall'
from CachingCallSite.java:207:in `call'
from CallThreeArgNode.java:61:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from RescueNode.java:216:in `executeBody'
from RescueNode.java:120:in `interpretWithJavaExceptions'
from RescueNode.java:110:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:169:in `call'
from DefaultMethod.java:171:in `call'
from RubyClass.java:522:in `finvoke'
from RubyBasicObject.java:1667:in `send19'
from RubyKernel.java:2079:in `send19'
from RubyKernel$s$send19.gen:65535:in `call'
from JavaMethod.java:266:in `call'
from CachingCallSite.java:282:in `cacheAndCall'
from CachingCallSite.java:139:in `call'
from CallSpecialArgNode.java:67:in `interpret'
from IfNode.java:117:in `interpret'
from NewlineNode.java:103:in `interpret'
from RescueNode.java:216:in `executeBody'
from RescueNode.java:120:in `interpretWithJavaExceptions'
from RescueNode.java:110:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:233:in `call'
from DefaultMethod.java:195:in `call'
from CachingCallSite.java:302:in `cacheAndCall'
from CachingCallSite.java:173:in `call'
from CallSpecialArgNode.java:69:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from IfNode.java:119:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:233:in `call'
from DefaultMethod.java:195:in `call'
from CachingCallSite.java:302:in `cacheAndCall'
from CachingCallSite.java:173:in `call'
from CallTwoArgNode.java:59:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:120:in `call'
from InterpretedMethod.java:134:in `call'
from DefaultMethod.java:154:in `call'
from CachingCallSite.java:252:in `cacheAndCall'
from CachingCallSite.java:71:in `call'
from FCallManyArgsNode.java:60:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from RescueNode.java:216:in `executeBody'
from RescueNode.java:120:in `interpretWithJavaExceptions'
from RescueNode.java:110:in `interpret'
from ASTInterpreter.java:74:in `INTERPRET_METHOD'
from InterpretedMethod.java:147:in `call'
from DefaultMethod.java:163:in `call'
from CachingCallSite.java:262:in `cacheAndCall'
from CachingCallSite.java:105:in `call'
from CallNoArgNode.java:62:in `interpret'
from NewlineNode.java:103:in `interpret'
from RescueNode.java:216:in `executeBody'
from RescueNode.java:120:in `interpretWithJavaExceptions'
from RescueNode.java:110:in `interpret'
from BeginNode.java:83:in `interpret'
from NewlineNode.java:103:in `interpret'
from BlockNode.java:71:in `interpret'
from RootNode.java:129:in `interpret'
from ASTInterpreter.java:119:in `INTERPRET_ROOT'
from Ruby.java:698:in `runInterpreter'
from Ruby.java:2426:in `loadFile'
from ExternalScript.java:66:in `load'
from LoadService.java:273:in `load'
from RubyKernel.java:1081:in `loadCommon'
from RubyKernel.java:1073:in `load19'
from RubyKernel$s$0$1$load19.gen:65535:in `call'
from DynamicMethod.java:213:in `call'
from DynamicMethod.java:209:in `call'
from CachingCallSite.java:282:in `cacheAndCall'
from CachingCallSite.java:139:in `call'
from /home/leo/.rvm/gems/ruby-1.9.2-p180/bin/bundle:19:in `_file_'
from /home/leo/.rvm/gems/ruby-1.9.2-p180/bin/bundle:-1:in `load'
from Ruby.java:671:in `runScript'
from Ruby.java:575:in `runNormally'
from Ruby.java:424:in `runFromMain'
from Main.java:278:in `doRunFromMain'
from Main.java:198:in `internalRun'
from Main.java:164:in `run'
from Main.java:148:in `run'
from Main.java:128:in `main'
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