Can't Log in to Sonarr V3 After Upgrading

Sonarr version (exact version):
Mono version (if Sonarr is not running on Windows):
OS: Windows 10
Debug logs:
Description of issue: I have been trying to upgrade Sonarr V2 to V3 as V2 is now not supported by the NZB mobile app. I followed the instructions on the Sonarr site and the install works fine. When I launch Sonarr I cannot log in. I am 100% I am using the right user and passwords as I had to uninstall and go back to Sonarr V2 which worked fine.

I have manually replaced the back up files as I thought maybe this would be the cause but this has not given me any luck. I did do a back up right before upgrading also.

Any ideas what is going wrong?

Not sure how much time you want to spend on it, but the easy approach would be to just change the login to none in the config.xml and then set the password again from the GUI.