You will need to browse to the following location on the registry

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{FB6D8570-49B2-4FCF-9BE4-79A74369CF4D}\InprocServer32

Within here locate the Key that is correct for your version of MatterSphere. Delete all the other Keys in this folder, but please note that you will likely have a Key with a higher version stamp than your current version
 
After the additional Keys have been deleted you should find that the context menu has returned.

If this does not work, you will have to uninstall the MatterSphere frameworks and then reinstall it.