Recently restored one of our servers and I encountered this error while trying to view a report:
An unexpected error occurred while compiling expressions. Native compiler return value: ‘[BC2001] file ….
1. Solving this seems so easy, first check the identity of the AppPool where the website is running:
2. From the command prompt type: %windir% and look for the temp folder. Add read/write permission to temp folder of windows to user in step 1.
Note: In other cases the temp folder is located somewhere else, so to check where it’s located go to System Properties -> Advance -> Environment Variables. In the System Variables look for the TEMP or TMP: