Hi Folks, I would appreciate it if Kim Cooper or one of the other Microchip Engineers could look at this problem. I've just spent a frustrating two hours trying to figure out a problem with the MPLAB Simulator. The problem came down to 10 commented out lines in a stimulus file. When I originally created the file, I had commented out the data (for use later) like this: !12345 1 ! Some Comments explaining the Serial Stream !12346 0 !12347 1 Each time I would load this stimulus file, the data changes wouldn't show up and when I tried to leave MPLAB, I would get a GPF error. Other Stimulus Files would load and run fine. When I finally guessed that this was the problem (unfortunately, I complicated it by using DOS E/Edit to create the file and I searched through looking for bad characters), I changed these lines to: ! 12345 1 ! Some Comments explaining the Serial Stream ! 12346 0 ! 12347 1 With the blank after the exclamation, everything worked fine. What was weird about the whole thing was that occasionally, Windows would get trashed as well. Is this documented somewhere or was I just unlucky? Myke Avoiding precedents does not mean nothing should ever be done. It only means that nothing should ever be done for the first time - Sir Humphrey Appleby K.C.B.