I recently inherited an app that had a similar problem.
Everytime the app was compiled the compiler would complain that two vars were undefined. The previous coders simply ignored the complaint because they couldn't find where in the report the vars were referenced. I couldn't either, even using hacktool or find. So I cut and pasted the controls into a new report and recompiled. The error msg went away and the app works fine.
Nebraska Dept of Revenue