CATIA V5: "Unable to save data. Problem with writing to file system".

Do you have "write" access to the folder?

This might be an issue with hard disk or corrupted OS. I too had same problem. The remedy that worked for me is, you change store location to another hard drive or may be on external devices. Once everything is done, you can copy back to your desired location. Hope this helps you.

Also reinstalling your OS can eradicate this problem completely (I read in article while back)