NTLM proxy problems: Authentication state already initialized

When an attempt is made to build the maven-antrun-plugin, which uses the docck plugin, from within a corporate network using an NTLM proxy, the following exception below is thrown by commons-httpclient.

Google finds lots of references to this exception from around 2005, the fix is probably to depend on a more recent version of commons-httpclient.

[INFO] ------------------------------------------------------------------------
[ERROR] FATAL ERROR
[INFO] ------------------------------------------------------------------------
[INFO] Authentication state already initialized
[INFO] ------------------------------------------------------------------------
[INFO] Trace
java.lang.IllegalStateException: Authentication state already initialized
at org.apache.commons.httpclient.auth.AuthState.setPreemptive(AuthState.
java:119)
at org.apache.commons.httpclient.HttpMethodDirector.executeConnect(HttpM
ethodDirector.java:486)
at org.apache.commons.httpclient.HttpMethodDirector.executeWithRetry(Htt
pMethodDirector.java:390)
at org.apache.commons.httpclient.HttpMethodDirector.executeMethod(HttpMe
thodDirector.java:170)
at org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.jav
a:396)
at org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.jav
a:324)
at org.apache.maven.plugin.docck.AbstractCheckDocumentationMojo.checkURL
(AbstractCheckDocumentationMojo.java:470)
at org.apache.maven.plugin.docck.AbstractCheckDocumentationMojo.checkPom
Requirements(AbstractCheckDocumentationMojo.java:377)
at org.apache.maven.plugin.docck.AbstractCheckDocumentationMojo.checkPro
ject(AbstractCheckDocumentationMojo.java:295)
at org.apache.maven.plugin.docck.AbstractCheckDocumentationMojo.execute(
AbstractCheckDocumentationMojo.java:144)
at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPlugi
nManager.java:443)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(Defa
ultLifecycleExecutor.java:539)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalWithLi
fecycle(DefaultLifecycleExecutor.java:480)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.forkProjectLifecy
cle(DefaultLifecycleExecutor.java:896)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.forkLifecycle(Def
aultLifecycleExecutor.java:739)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(Defa
ultLifecycleExecutor.java:510)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeStandalone
Goal(DefaultLifecycleExecutor.java:493)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(Defau
ltLifecycleExecutor.java:463)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHan
dleFailures(DefaultLifecycleExecutor.java:311)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegmen
ts(DefaultLifecycleExecutor.java:278)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLi
fecycleExecutor.java:143)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:334)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:125)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:272)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.
java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
sorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
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)