Monodevelop wont open Unity 5

Windows 7.1 ULT 64bit
.Net Framework 4.5.1
PlayStationMobile (with MonoDevelop 2.8.8.4)
Norton 360

When attempting to open a script for editing the MonoDevelop 4.0.1 splash pops up twice but nothing more.

Task manager shows there are no monodevs running in the background.

I have read a number of other similar posts but have not identified a solution.

Found the solution in this post http://answers.unity3d.com/answers/574295/view.html

Solved it by downloading this file and putting it in the Unity\Monodevelop\bin folder. Don’t forget to make a backup of the original file, for the heck of it.

“This file” fixed it for me.