Logon error to readonly db
So on the SQL server, I was able to go to the "Event Viewer -> Windows Logs -> Application" and was able to match the event time with my time stamp in the SQL error log. 
Then i was able to find the user that was causing the error.
Since we have a newly introduced AlwaysOn environment we went through his options to make sure it was set up correctly, that didn't help.

The issue was that he was on an old verision of SSMS that when he tried to connect seemed to cause the error. We updated his SSMS to latest version and it stopped.