Dear Bruce,
        I would reinstall your Cas 3.10 program.  The problem is
occurring on your PC and has nothing to do with the Mac's, or B.) blame
the zip drive, where you a getting write errors.  This can be caused by
a bad scsi cable, the zip scsi card, or a bad mother board.  Also, you
could test this with Cas 2.5 instead of 3.10.  If the problem continues
it is the zip and computer mother board.  You could also test this by
ftping files from the PC hard drive to a central server then download.
If these open without any problems, it points to the zip as the problem.
I personally hate zips.  They tend to be  very problematic, so I have
banned them from my facility. We use a large central file server, that
serves as a temporary holding site for all images.  Users  download
these over the network via ftp.  Works great and serves all platforms.
Our archival is done on 4.6 Gig optical disks,  600 opticals, or 640
MOs.  These are far more reliable, and I have not lost any data from
these in over 5 years.

Joe Goodhouse
Confocal / EM Core Facility
Molecular Biology