Installing the plugin using the grails command on 1.1-RC1 works without a problem.

However,

mvn archetype:generate -DarchetypeGroupId=org.grails -DarchetypeArtifactId=grails-maven-archetype -DarchetypeVersion=1.0-SNAPSHOT -DarchetypeRepository=http://snapshots.repository.codehaus.org -DgroupId=org.grails -DartifactId=jquery-plugin-test
mvn initialize
mvn grails:install-plugin -DpluginName=jquery

results in the following exception:

luis@trinity:~/pilango-workspace/grails-stuff/jquery-plugin-test$ mvn grails:install-plugin -DpluginName=jquery
[INFO] Scanning for projects...
[INFO] Searching repository for plugin with prefix: 'grails'.
[INFO] ------------------------------------------------------------------------
[INFO] Building Unnamed - org.grails:jquery-plugin-test:war:1.0-SNAPSHOT
[INFO] task-segment: [grails:install-plugin] (aggregator-style)
[INFO] ------------------------------------------------------------------------
[WARNING] Attempting to build MavenProject instance for Artifact (org.grails:grails-maven-plugin:1.0-20090210.081513-8) of type: maven-plugin; constructing POM artifact instead.
[INFO] [grails:install-plugin]
Running pre-compiled script
Environment set to development
Reading remote plugin list ...
Reading remote plugin list ...
Plugin list out-of-date, retrieving..
[delete] Deleting: /home/luis/.grails/1.1-SNAPSHOT/plugins-list-default.xml
[get] Getting: http://plugins.grails.org/.plugin-meta/plugins-list.xml
[get] To: /home/luis/.grails/1.1-SNAPSHOT/plugins-list-default.xml
..........................................................................................................................................
[get] last modified = Tue Feb 24 11:34:09 CET 2009
[copy] Copying 1 file to /home/luis/pilango-workspace/grails-stuff/jquery-plugin-test/plugins
Installing plug-in jquery-1.0RC2b
[mkdir] Created dir: /home/luis/pilango-workspace/grails-stuff/jquery-plugin-test/plugins/jquery-1.0RC2b
[unzip] Expanding: /home/luis/.grails/1.1-SNAPSHOT/plugins/grails-jquery-1.0RC2b.zip into /home/luis/pilango-workspace/grails-stuff/jquery-plugin-test/plugins/jquery-1.0RC2b
Executing jquery-1.0RC2b plugin post-install script ...
java.lang.RuntimeException: java.io.FileNotFoundException: /home/luis/pilango-workspace/grails-stuff/jquery-plugin-test/null/scripts/Init.groovy (/home/luis/pilango-workspace/grails-stuff/jquery-plugin-test/null/scripts/Init.groovy)
at Script1.run(Script1.groovy:16)
at _PluginDependencies$_run_closure19.doCall(_PluginDependencies.groovy:547)
at _PluginDependencies$_run_closure26.doCall(_PluginDependencies.groovy:795)
at _GrailsPlugins.completePluginInstall(_GrailsPlugins.groovy:80)
at _GrailsPlugins.this$4$completePluginInstall(_GrailsPlugins.groovy)
at _GrailsPlugins$this$4$completePluginInstall.callCurrent(Unknown Source)
at _GrailsPlugins.withPluginInstall(_GrailsPlugins.groovy:68)
at _GrailsPlugins.this$4$withPluginInstall(_GrailsPlugins.groovy)
at _GrailsPlugins$_run_closure4.doCall(_GrailsPlugins.groovy:60)
at _GrailsPlugins$_run_closure5.doCall(_GrailsPlugins.groovy:110)
at gant.Gant$_dispatch_closure4.doCall(Gant.groovy:324)
at gant.Gant$_dispatch_closure6.doCall(Gant.groovy:334)
at gant.Gant$_dispatch_closure6.doCall(Gant.groovy)
at gant.Gant.withBuildListeners(Gant.groovy:344)
at gant.Gant.this$2$withBuildListeners(Gant.groovy)
at gant.Gant$this$2$withBuildListeners.callCurrent(Unknown Source)
at gant.Gant.dispatch(Gant.groovy:334)
at gant.Gant.this$2$dispatch(Gant.groovy)
at gant.Gant.invokeMethod(Gant.groovy)
at gant.Gant.processTargets(Gant.groovy:495)
at gant.Gant.processTargets(Gant.groovy:480)
at org.grails.maven.plugin.AbstractGrailsMojo.runGrails(AbstractGrailsMojo.java:223)
at org.grails.maven.plugin.GrailsInstallPluginMojo.execute(GrailsInstallPluginMojo.java:84)
at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:451)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:558)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeStandaloneGoal(DefaultLifecycleExecutor.java:512)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(DefaultLifecycleExecutor.java:482)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:330)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:227)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:142)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:336)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:129)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:287)
at org.codehaus.classworlds.Launcher.launchEnhanced(Launcher.java:315)
at org.codehaus.classworlds.Launcher.launch(Launcher.java:255)
at org.codehaus.classworlds.Launcher.mainWithExitCode(Launcher.java:430)
at org.codehaus.classworlds.Launcher.main(Launcher.java:375)
Caused by: java.io.FileNotFoundException: /home/luis/pilango-workspace/grails-stuff/jquery-plugin-test/null/scripts/Init.groovy (/home/luis/pilango-workspace/grails-stuff/jquery-plugin-test/null/scripts/Init.groovy)
... 37 more
Error installing plugin: java.io.FileNotFoundException: /home/luis/pilango-workspace/grails-stuff/jquery-plugin-test/null/scripts/Init.groovy (/home/luis/pilango-workspace/grails-stuff/jquery-plugin-test/null/scripts/Init.groovy): java.io.FileNotFoundException: /home/luis/pilango-workspace/grails-stuff/jquery-plugin-test/null/scripts/Init.groovy (/home/luis/pilango-workspace/grails-stuff/jquery-plugin-test/null/scripts/Init.groovy)