I don't know if somebody already had this kind of error, but when I open a drawing model and click at the "select sheets to open..." and fix just one sheet to load. Until now nothing interesting having, but if I modify only this sheet, save and close. When I try to open again the same drawing that I saved the following error appears "An unknown error occurred while accessing (address of the file) ". I have the SolidWorks 2012 sp 3.0. Could someone help me with this problem?