I have a compiled key scan program I wrote using the latest full version of C51. I went to the debugger (added my variables to watch window 1) and ran the code successfully. I returned to uVisionII. After looking the code over (no changes) I returned back to the debugger for a more thorough test of the code. Now debug refuses to accept some of the variables it previously accepted. I get an error 34 'undefined identifier' any time I try to add (specific variables) to the watch window. I'm using XP Pro. Is this a bug or what? Please help Brian