Help! I just can't figure this out. Suddenly I can't add custom properties to my files. I can save this assembly after making changes to the hardware components, but as soon as I add my standard custom properties to populate the drawing I get the message "An unknown error occurred while accessing "filename". If I blank the custom properties I don't have any issues and can save the file.  Adding even one (of 10) does the same thing.

I edited the custom properties once to bring them from 2011 to 2012 just in case. All my default file locations are correct too. SW 2012 SP1