The most likely cause of the problem you describe is a corrupted directory structure. This type of problem could happen either on an AppleShare server or an individual Macintosh. Here is what we suggest:
1) Use Disk First Aid on the volume; this will sometimes repair slightly damaged directories.
2) Run "The Norton Utilities for the Macintosh", "Symantec Utilities for the Macintosh", or equivalent package to try to repair the volume. These utilities can repair damaged directories that Disk First Aid cannot.
3) Back up all the data on the hard disk and reformat it. This will solve the problem if all else fails.