title: Cannot access EWS from Outlook add-in
body: <p>For the last few months I have been learning how to write an Outlook add-in.  Using the standard solution generated from Visual Studio as a base and connecting to my Office 265 mailbox I managed to create a nice little working app. I then started to add some EWS calls 
  into the app and that, too, was going well until it suddenly stopped working. The makeEwsRequestAsync method would return 'successful' and nothing else no matter what i passed to it, including rubbish. I tried running my code on another PC with the same Office 365 account 
  and that, too, would not return any data from the makeEwsRequestAsync method. 
  I created a new solution and ran it exactly as VS 2017 generated it. Appeared to run OK but my app icon did not appear in my mail item no matter whether i ran outlook on my desktop or in a browser. 
  The windows application log had this message:</p>
  
  <p>The Exchange web service request GetAppManifests failed. The error code is 4. 
  HTTP Response Code: 200</p>
  
  <p>Additional Error Message: 
  Properties couldn't be set.
   Exception = Microsoft.Mapi.MapiExceptionPartialCompletion: MapiExceptionPartialCompletion: SetProps had property problems (hr=0x40680, ec=0) Diagnostic context:     Lid: 55847   EMSMDBPOOL.EcPoolSessionDoRpc called [length=146]     Lid: 43559   EMSMDBPOOL.EcPoolSessionDoRpc returned [ec=0x0][length=320][latency=1]     Lid: 52176   ClientVersion: 15.20.1665.20     Lid: 50032   ServerVersion: 15.20.1665.6020     Lid: 35180       Lid: 23226   --- ROP Parse Start ---     Lid: 27962   ROP: ropSetProps [10]     Lid: 27962   ROP: ropExtendedError [250]     Lid: 1494    ---- Remote Context Beg ----     Lid: 38698       Lid: 32392   qdwParam: 0x8D6A17A3F400B6C      Lid: 56793   dwParam: 0x0     Lid: 50200   StoreEc: 0x80040604     Lid: 45434   Guid: bf41dd79-71de-4c8a-897d-f6f09c06b333     Lid: 10786   dwParam: 0x0        Msg: 15.20.1665.020:VI1PR0201MB2224:d870c918-923e-41bf-85d1-4b1315b6f04f     Lid: 1750    ---- Remote Context End ----     Lid: 31418   --- ROP Parse Done ---. MapiExceptionPartialCompletion: SetProps had property problems (hr=0x40680, ec=0) Diagnostic context:     Lid: 55847   EMSMDBPOOL.EcPoolSessionDoRpc called [length=146]     Lid: 43559   EMSMDBPOOL.EcPoolSessionDoRpc returned [ec=0x0][length=320][latency=1]     Lid: 52176   ClientVersion: 15.20.1665.20     Lid: 50032   ServerVersion: 15.20.1665.6020     Lid: 35180       Lid: 23226   --- ROP Parse Start ---     Lid: 27962   ROP: ropSetProps [10]     Lid: 27962   ROP: ropExtendedError [250]     Lid: 1494    ---- Remote Context Beg ----     Lid: 38698       Lid: 32392   qdwParam: 0x8D6A17A3F400B6C      Lid: 56793   dwParam: 0x0     Lid: 50200   StoreEc: 0x80040604     Lid: 45434   Guid: bf41dd79-71de-4c8a-897d-f6f09c06b333     Lid: 10786   dwParam: 0x0        Msg: 15.20.1665.020:VI1PR0201MB2224:d870c918-923e-41bf-85d1-4b1315b6f04f     Lid: 1750    ---- Remote Context End ----     Lid: 31418   --- ROP Parse Done ---</p>
  
  <p>I tried my new app against a different mailbox and it worked fine.</p>
  
  <p>Is it possible that my mailbox has been blocked from EWS?</p>