I too have backup problems with First Edge. It used to work but no longer does. I have a Mac. The Save button is greyed out so I can not do the backup.
I just loaded FirstEdge on a Mac (10.5.4) and created a new company file. I too receive the 'greyed-out' save button when backing up the file. If I manually edit the MYOB supplied 'save-as' file name, the save button becomes enabled, and I can create a backup. Not an ideal solution, but it seems to work for me.