*.cdr was modified by another user since you opened the file

Corel 7.3, Win 7 64bit. 

Suddenly im getting the message below when saving.    Sometimes it happens instantly other times I get a couple of saves before it pops up.  Its massively annoying as saving progress means i have use saves as with a new file name every time.

There is only 1 corel user and only 1 windows user (Admin) for the PC Im working on.

Any suggestions?