I just tried this and encountered a problem.
After successfully creating a RM4 backup (used the default filename with the .rmgb extension), I attemped to restore the data base. When I selected the .rmgb file I just created and pressed the "Begin Restore..." button, a RM4 window popped-up that stated " You must enter a valid filename for the backup" - something's broke...

I have the same problem as of this morning after I installed the latest RM4 update. I always use the default file name and when I tried to restore my latest backup I got the same message to enter a valid file name. To restore I did what I always do - clicked File, Restore and chose the latest backup which is SCOTT (2009-03-21).rmgb. Hope someone can help!