"Already exists" SVN error during release:branch

~/releases/trunks/platform/web$ mvn release:branch -DbranchName="xwiki-web-1.9" -DautoVersionSubmodules=true -e
+ Error stacktraces are turned on.
[INFO] Scanning for projects...
[INFO] Reactor build order: 
[INFO]   XWiki Platform - Web - Parent POM
[INFO]   XWiki Platform - Web - GWT API
[INFO]   XWiki Platform - Web - GWT - DOM API
[INFO]   XWiki Platform - Web - WYSIWYG
[INFO]   XWiki Platform - Web - Standard
[INFO]   XWiki Platform - Web - Exo
[INFO] Searching repository for plugin with prefix: 'release'.
[INFO] ------------------------------------------------------------------------
[INFO] Building XWiki Platform - Web - Parent POM
[INFO]    task-segment: [release:branch] (aggregator-style)
[INFO] ------------------------------------------------------------------------
[INFO] [release:branch]
[INFO] Verifying that there are no local modifications...
[INFO] Executing: /bin/sh -c cd /home/hudsonagent/releases/trunks/platform/web && svn --non-interactive status
[INFO] Working directory: /home/hudsonagent/releases/trunks/platform/web
What is the new working copy version for "XWiki Platform - Web - Parent POM"? (com.xpn.xwiki.platform:xwiki-web) 1.10-SNAPSHOT: : 2.0-SNAPSHOT
[INFO] Transforming 'XWiki Platform - Web - Parent POM'...
[INFO] Transforming 'XWiki Platform - Web - GWT API'...
[INFO] Transforming 'XWiki Platform - Web - GWT - DOM API'...
[INFO] Transforming 'XWiki Platform - Web - WYSIWYG'...
[INFO] Updating xwiki-web-gwt to 1.9-SNAPSHOT
[INFO] Ignoring artifact version update for expression: ${pom.version}
[INFO] Updating xwiki-web-gwt to 1.9-SNAPSHOT
[INFO] Ignoring artifact version update for expression: ${pom.version}
[INFO] Updating xwiki-web-gwt-dom to 1.9-SNAPSHOT
[INFO] Ignoring artifact version update for expression: ${pom.version}
[INFO] Transforming 'XWiki Platform - Web - Standard'...
[INFO] Updating xwiki-web-gwt to 1.9-SNAPSHOT
[INFO] Ignoring artifact version update for expression: ${pom.version}
[INFO] Updating xwiki-web-wysiwyg to 1.9-SNAPSHOT
[INFO] Ignoring artifact version update for expression: ${pom.version}
[INFO] Transforming 'XWiki Platform - Web - Exo'...
[INFO] Updating xwiki-web-standard to 1.9-SNAPSHOT
[INFO] Ignoring artifact version update for expression: ${pom.version}
[INFO] Checking in modified POMs...
[INFO] Executing: /bin/sh -c cd /home/hudsonagent/releases/trunks/platform/web && svn --non-interactive commit --file /tmp/maven-scm-437470090.commit --targets /tmp/maven-scm-11976-targets
[INFO] Working directory: /home/hudsonagent/releases/trunks/platform/web
[INFO] Branching release with the label xwiki-web-1.9...
[INFO] Executing: /bin/sh -c cd /home/hudsonagent/releases/trunks/platform/web && svn --non-interactive copy --file /tmp/maven-scm-1089525731.commit . https://svn.xwiki.org/svnroot/xwiki/platform/web/branches/xwiki-web-1.9
[INFO] Working directory: /home/hudsonagent/releases/trunks/platform/web
org.apache.maven.shared.release.scm.ReleaseScmCommandException: Unable to branch SCM
Provider message:
The svn branch command failed.
Command output:
svn: Commit failed (details follow):
svn: File '/svnroot/xwiki/platform/web/branches/xwiki-web-1.9/wysiwyg/pom.xml' already exists

	at org.apache.maven.shared.release.phase.ScmBranchPhase.execute(ScmBranchPhase.java:98)
	at org.apache.maven.shared.release.DefaultReleaseManager.branch(DefaultReleaseManager.java:382)
	at org.apache.maven.shared.release.DefaultReleaseManager.branch(DefaultReleaseManager.java:353)
	at org.apache.maven.plugins.release.BranchReleaseMojo.execute(BranchReleaseMojo.java:133)
	at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:458)
	at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:676)
	at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeStandaloneGoal(DefaultLifecycleExecutor.java:551)
	at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(DefaultLifecycleExecutor.java:521)
	at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:369)
	at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:266)
	at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:181)
	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:302)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.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)
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Unable to branch SCM
Provider message:
The svn branch command failed.
Command output:
svn: Commit failed (details follow):
svn: File '/svnroot/xwiki/platform/web/branches/xwiki-web-1.9/wysiwyg/pom.xml' already exists

[INFO] ------------------------------------------------------------------------
[INFO] Trace
org.apache.maven.BuildFailureException: Unable to branch SCM
Provider message:
The svn branch command failed.
Command output:
svn: Commit failed (details follow):
svn: File '/svnroot/xwiki/platform/web/branches/xwiki-web-1.9/wysiwyg/pom.xml' already exists

	at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:697)
	at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeStandaloneGoal(DefaultLifecycleExecutor.java:551)
	at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(DefaultLifecycleExecutor.java:521)
	at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:369)
	at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:266)
	at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:181)
	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:302)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.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)
Caused by: org.apache.maven.plugin.MojoFailureException: Unable to branch SCM
Provider message:
The svn branch command failed.
Command output:
svn: Commit failed (details follow):
svn: File '/svnroot/xwiki/platform/web/branches/xwiki-web-1.9/wysiwyg/pom.xml' already exists

	at org.apache.maven.plugins.release.BranchReleaseMojo.execute(BranchReleaseMojo.java:142)
	at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:458)
	at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:676)
	... 16 more
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 10 seconds
[INFO] Finished at: Tue May 12 10:07:22 GMT+01:00 2009
[INFO] Final Memory: 10M/77M
[INFO] ------------------------------------------------------------------------