CreatePASEAR weirdness

Yesterday I encountered a weird problem. My creation of an EAR file using the CreatePASEAR tool stopped working, generating an ANT error 'Unable to delete file':

Unable to delete file C:\Temp\cps\cps_source.ear
        at org.apache.tools.ant.taskdefs.Delete.execute(Delete.java:449)
        at com.tibco.ps.anttasks.utils.AntTaskUtils.deleteFile(AntTaskUtils.java
:129)
        at com.tibco.ps.anttasks.deployment.GenericPSBasedEARTask.execute(Unknow
n Source)
        at org.apache.tools.ant.Task.perform(Task.java:341)
        at org.apache.tools.ant.Target.execute(Target.java:309)
        at org.apache.tools.ant.Target.performTasks(Target.java:336)
        at org.apache.tools.ant.Project.executeTarget(Project.java:1339)
        at org.apache.tools.ant.Project.executeTargets(Project.java:1255)
        at com.tibco.ps.anttasks.TIBCOMain.a(TIBCOMain.java:618)
        at com.tibco.ps.anttasks.TIBCOMain.start(TIBCOMain.java:186)
        at com.tibco.ps.anttasks.TIBCOMain.main(TIBCOMain.java:225)

After much investigation, it turns out the this error is bogus - it is generated by the tool during clean-up operations after the real error has happened. The actual error was malformed XML in my web.xml file (the CreatePASEAR file rewrites the web.xml during EAR generation).

The real error can be found in the TIBCO_HOME/portal/5.1/logs/utils/PortalUtils.log, for example:

[createPASEAR] Caused by: Failed to parse descriptor: Next character must be ">" terminating comment .
[createPASEAR]  at org.apache.cactus.integration.ant.WebXmlMergeTask.execute(WebXmlMergeTask.java:142)
[createPASEAR]  at com.tibco.ps.anttasks.deployment.TIBCOWebXmlMergeTask.execute(Unknown Source)
[createPASEAR]  ... 17 more
[createPASEAR] Caused by: org.xml.sax.SAXParseException: Next character must be ">" terminating comment .
[createPASEAR]  at org.apache.crimson.parser.Parser2.fatal(Parser2.java:3376)
[createPASEAR]  at org.apache.crimson.parser.Parser2.fatal(Parser2.java:3370)

I hope this helps someone from enduring the hours of frustration I had trying to find a bogus file permission/locking problem!