[DaveHorn]

Free space is not a problem. I have far less space available on my HDs and run OOTP/Cato without any issues.

If other applications like OOTP are running and working off the same hard drive than the drive isn't likely experiencing a general failure.

I think its one of two things; a red herring error from catobase that has nothing to do with your hard drive, or possibly you have a bad sector on the disk and when cato tries to write data to that sector is chokes out. Utilities such as scandisk (and maybe even chkdsk /R ) will locate and mark bad sectors so the OS doesn't write to them anymore.