Does anyone know what would cause a concurrency build issue in an xml file in xdocs that previously had never generated a build or run issue, is generated properly by the server in run, yet on build, fails with the messages:

java.util.ConcurrentModificationException: File ...is already beng written by another thread

and the packages/class/methods that are unhappy:
org.apache.excalibur.source.impl.FileSource.getOutputSteam(FileSource.java
org.apache.cocoon.bean.CocoonBean.processTarget(CocoonBean.java)
org.apache.cocoon.bean.CocoonBean.process(CocoonBean.java)

the next forrest output is
[dir/file] BROKEN: URI not found: File [path][dir/file] is already being written by another thread

There are no entries in my logs to offer hints on this.
I stopped/started the server, cleared cache, checked the file, it is just standard text/xdoc, the only place it is called is site which is correct. THis came out of no where.
using F0.7
cheers,
helena