Comment 8 for bug 1682779

I had the same problem this morning, and was close to changing to some other development environment, until an memory came to me.

I remembered the night before, I had been doing some system maintenance, and for some odd reason, I felt a need to rename the projects folder from "mono projects" to "mono-projects".

So before trying to open a previous project again, I opened the preferences window for MonoDevelop, (edit>preferences) and under the "Projects>Load/Save" section, there it was... it still had the original folder name in the "Default Solution location" text-box.

So I added the hyphen, saved it, and restarted MonoDevelop ... now it's back to working like a champ.

Hope that helped, or at least gave someone the hint needed to find their own solution.