Can't open any scripts in MonoDevelop in b6

When I try to open any C# script in MonoDevelop, I get the following error (also see the attached screenshot):

The same happens in all projects, old and new, so I don’t know if a bug report would be useful. Also tried to completely uninstall and reinstall Unity, but it didn’t help. I installed the 64 bit editor and I’m on Windows 8.1.

Just noticed that the error is listed in known issues in the release notes. I have to wonder why a release is made with such a crippling issue.

Also, even if I had noticed the issue in the release notes before downloading, it probably wouldn’t have raised any alarm bells, since it doesn’t mention that the error also renders MonoDevelop completely unusable.