The file 'filename' could not be opened for editing. It may be in use by another process.
This error message can be generated in projects of many types, regardless of whether they include a policy file.
To solve this problem
Determine whether another process is open that could be using the file you want to open.
Close the process.
Try to open the file again. If you receive this error message again, repeat steps 2 and 3 until you locate the process creating the problem.