well. i finally refactored the code and made a lot of subVIs so it is was more readable and after that the error was gone. i never changed anything, just selected chunks of code and hit edit>make subVI... and it worked after that. no idea what happened. but im glad it is finally solved. NI should check my VI though. cause if it wasn't just my computer then a lot of errors could happen if LabVIEW can't make a simple substract. thank you very much for your help. 🙂