[MonoDevelop] ERROR Message: Corlib not in sync with this runtime: expected corlib version 632, found 96

[Megan Clodfelter]

Just upgraded and now I can't compile - I did a clean all, build all, and I fail with the above message
MonoDevelop 3.0.3.4
Mono 2.10.9 
Monotouch: 5.3.5

I've restarted my machine - clean, build etc.  Same error
I created a new project - clean, build, same error

How do I uninstall and return to a version that works?