After upgrading to monodevelop 5.3 from git I could no longer load asp projects. I always received the following error.
Could not load type 'MonoDevelop.AspNet.AspNetAppProject' from assembly 'MonoDevelop.AspNet
There is a quick fix. Disable and renable the monodevelop asp add-ins.
Tools -> Add-in Manager ->Web Development
Disable and enable all web add-ins. Reload your solution and it should work.