An error occurred

One of the most frustrating things in the Skype for Business client is lack of meaningful error messages.

We have an on-prem environment and a user adds a colleague to a Skype call. All PC to PC. Then they get "An error occurred". No clue as to what the error is. No codes. Nothing.

However, this seems to be it for this client. I have the logs. I know which users are involved. I suspect this is the url that is storing the metadata on the server side. However, if anyone has any ideas of the sort of things I should look for in the logs then that would be of great help.

Unfortunately I can't post the log here. 

Just want some ideas.