To reproduce:
1. Have the previous version of Unity installed in "Unity" version
2. Install the latest Unity version on your Mac (without changing the installation folder)
3. Make sure that no MonoDevelop app instances are open
4. Open Unity
5. Create a new project
6. Create a new script by right-clicking in the project view "Create -> C# script"
7. Double-click on the script
8. Errors are thrown

9. After clicking "OK" on all of the dialogs that popped-up you will notice that the solution is not loaded

10. Open the same script with some other external editor
11. Include a compiler error in it (write any C#-illegal sentence)
12. Save the script and close it
13. Notice the error thrown in the console (compiler error)
14. Double-click on the error
15. Normally, the previous action should open the script with MonoDevelop and move the cursor to the line where the error is. Notice, that the cursor is at the beginning of the script