please do three things.
1: give us the sourcecode for the function this occurs in.
2: tell us which qccompiler you are using
3: tell us which engine you are using (not really the engine's fault, but helps for debugging).
I believe this most commonly happens as the result of a mismatched type in a function call somewhere, so make sure you fix the warnings your qcc gives (and if it doesn't give any, use frikqcc or fteqcc).