Some users may receive this error when the Shared Documents folder is set with incorrect permissions. For more information, please see this Microsoft KB article regarding the issue.
- Download the attached fixpermissions.zip file and uncompress it (the zip file password is torchlight).
- Double-click to run fixpermissions.bat
- After it finishes running, try launching Torchlight again and enter your key.
If you receive further error messages, or the game doesn't launch, you may need to reboot your computer into Safe Mode in order to run this fix. For information about how to boot into Safe Mode, please see this Microsoft KB Article.