Running Outlook 2011 under OS 10.10.5 but now Outlook 2011 no longer opens on this computer that also has Outlook 2016 installed. Upon starting Outlook 2011, the opening splash screen doesn't even consistently appear and the "active" notation dot in the Dock appears for a short time but then disappears. I get no error message. One time after I moved the current 2011 Main Identity to the trash (but did not empty the trash) I was told that I had to select an Identity.

Thus I've tried using backup Main Identities and they do not work either. I was able to import the current Outlook 2011 Main Identity into Outlook 2016 with no issues and CAN access my Exchange server email account using Outlook 2016.

I've twice repaired disk permissions and restarted after each repair but still cannot open Outlook 2011 on that computer.  I CAN open Outlook 2011 on my other computer (under OS 10.10.5) and CAN access my Exchanger server email account via that computer. The 2nd computer does NOT have Outlook 2016 installed. 

Does Outlook 2016 interfere with Outlook 2011? If not, does this mean I'd need to reinstall Office 2011 on the first computer to get it to continue working?