Where is the disk located?
I had a "strange" bug when writing files to a USB disk, that did not appear when writing directly to the hard drive. I would create a file, write a header to a that file, then close it, and open it in another VI. This was all done sequentially with error wires and such connecting the VIs. For some unknown reason, maybe caching, when running the program through files on a USB disk after closing the file I would get an error "This file does not exist" when trying to use it for the next part of the program. The error was random and would occur at any point in the batch processing of files. The solution was to make a small loop with a delay that checked if the files existed before going to the next step. I know this doesn't exactly help, but maybe it will give you some ideas.
mcduff
