I access a remote repo for a company I do a lot of work with. The repo's been active for a long time and I use it regularly. After I downloaded the latest update, I open Sourcetree and click the remote tab. It asks me to authenticate my Github account which I do and I get the error message: 

message: Requires authentication

https://developer.github.com/v3/repos/#list-your-repositories

I click 'sign-in' and add my credentials which are accepted and gives me a 'Authorize SourceTreeForMac screen and lists the repo but the 'Authorise Atlassian' button is disabled