Please try the following steps to troubleshoot this error:
1. Clear the temp folder on the end users machine, by default C:\Documents and Settings\
2. Check to see if any of the files has one of the following special characters in the filename, and remove these characters if they occur: / \ | : * ? " < >
3. Then try to save the scenario again. If the problem persists, please have the user save the objects which make up the scenario as individual files (*. pwo, *.pmo, *.pco) files if possible, and send them to us for review. We will then work to recreate the issue on our end and propose additional steps to correct the problem.