Unable to delete hashed file - job aborts

[Nic]

Error message - every job aborts which has a hashed file in it

FSSValidationJob..HshFSS.LnkToHshFSS: DSD.UVOpen rm: Unable to remove directory HshFSS: File exists
Unable to DELETE file "HshFSS".
"HshFSS" is already in your VOC file as a file definition record.
File name =
File not created.
.

I have a batch job that has been running fine on Project A for about 2-3 weeks until it suddenly started aborting with the above message. Every job that had a hashed file aborted. When I exported the batch and used another project it was running fine.
A month later this problem occurred on the other project. The 3am schedule was running fine but when it came to manually running the batch job in the morning it started aborting. The batch job has been scheduled for 3am every night for about a week now and additionally we have been running it 3-4 times a day as well without any problems.
I am using dynamic hashed files, that are deleted and recreated every time the job is run in the default project directory. Apparently this isn't a space issue. There is other development work going on in the same project but the file names are different.
Any idea what could be causing this problem. I am more interested in the preventing rather than the resolving at this stage.
Thanks very much for your help.