Hi,
I ran into this problem the same as you did. What a terrible feeling not being able to open my database for 5+ hours, I had spent so much time on it.
This problem seems to pertain to databases with a custom ribbon! The front end is looking for USysRibbons linked in the back end but cannot get it, causing the program to fail.
The answer to this problem seems to be you have to get the front and back end linked just the way they were so you can get back into your front end. I was fortunate enough to remember how to get them linked up just the way they were on the same network setup.
You must move the USysRibbons table from being linked to the backend to just being in the front end. Then you will be able to open your database without the link being made.
Check microsoft support kb 926533, the forum won't let me post the link.
I had been accessing my database for years, and knew if the link was bad I had to get it working again otherwise I could not access the front end but never really thought of the implications. When my server had moved and everything had been changed I easily realized the implications. The link was not easy to remake.