Heres a challenge for you!!

We've had an intermittent bug that has been occurring on our test machines for about 3 months now. It started out as just a simple little "File does not exist" error, which of course didn't tell us much of anything. The error occurs occasionally when previewing or printing a report. The problem is compounded by the fact that we can't seem to get the error to repeat in developement mode in order to track it to a specific line or procedure. In response we put in a whole bunch of error handlers to give us more descriptive errors. We have finally tracked the problem to the following line (we think):
use (tc_ReportName) alias OldReport
where tc_ReprotName is the name of the frx file. Why would we be opening an frx table, you ask? In order to clear the tag and tag2 fields of printer information. We actually starting doing this in response to the original "File does not exist" error. The error message we get now is "File 'c:\sxxi\masschangesummary.frx' does not exist" where sxxi is the directory we are running the program out of.
Does anyone have any idea why an executable would not be able to find an frx file?
Any suggestions or clues are appreciated.
Alex