Have you tried a forward merge?
Open a new and reset file in 9.
Merge the bad file into it.
Often this works.
You will lose and info added in section and elevation windows, but the model will be saved as well as info in plan windows.
Good Luck.
If this doesn't work, send to Graphisoft.
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"