I've spent the morning trying to analyze where in code the ISOs are occurring in a large vfp6 app which runs fine in Win9x, but not NT4, looking for a pattern. The ISOs are always table-related, on lines of code like USE mytable, LOCATE, REPLACE, SQL SELECT, etc. One thing that I found was that periodically the ISO is followed by a "cannot update the cursor" for no apparent reason, but I think this is an important clue. Any ideas?