I already have access (in fact as an Admin) to Cloud Jira, Confluence and Bitbucket and have been using them for months and have had no problem logging in.
I now wanted to install Sourcetree, so downloaded the latest install (version 2.1.2.5) and ran it. As part of the install, it requires you to log in to your Atlassian account, which I thought would be easy, except I get the message below

Unfortunately the few minutes mentioned in the error message has stretched into hours since yesterday.
I've cleared the cache in my browser, I've tried staying logged in on MyAtlassian, I've tried rebooting the PC, but still get the same message.
Has anybody had / having a similar issue? Any ideas on how to resolve?
Thanks