If you checkout the trunk to a folder long than /tmp (in my case it is "/home/adrian/workspace/hadoop-trunk") and you execute the command:
ant clean package
You get the following error:
/home/adrian/workspace/hadoop-trunk/build.xml:730: Execute failed: java.io.IOException: Cannot run program "chmod": java.io.IOException: error=7, Argument list too long
I also tried this from the folder "/tmp/trunk" and the package target worked fine so I imagine the argument list is becoming too long due to the folder being longer. A simple fix for this should be to set the "parallel" attribute on chmod to false.