I'm using Hudson with Ant+ivy and many jobs which starts in parallel. My problem is that I use a cache folder for Ivy which is deleted and updated in the ant task of every job.
Of course, several builds fail because they can't delete the ivy folder and some other fail because the can't find the libraries being deleted at the same time.
BUILD FAILED
C:\dev.hudson\jobs\api\workspace\build\build.xml:100: Unable to delete the directory C:\dev\tools\build\ant\extensions\ivy\cache\myapp
and
BUILD FAILED
C:\dev.hudson\jobs\api\workspace\build\build.xml:104: impossible to resolve dependencies: resolve failed - see output for details