I recently ran into this notorious error message when working in Studio 2015 and did the usual workarounds, i.e., exiting and reopening Studio, re-creating projects, re-creating TMs, deleting and reinstalling Studio, refreshing the view, etc. but nothing seemed to work. Sometimes Studio freezes or parts are blanked out. Sometimes I get the error message: Key not found […] Parameter name: Key. I am able to use a legacy version of Studio (Studio 2011) for some reason. I have already lost half a day. Help!