Upgrade to APEX 4.1: Invalid Login Credentials

Always a good idea to upgrade on a Friday.. not

Always a good idea to upgrade on a Friday.. not… In the past I did numerous upgrades to the latest APEX release, and never really encountered big problems. It was always very smooth, kudos to the APEX-team. If something went wrong it was mostly my own fault, which I will admit now. Because of the history of going very smoothly, I dare to do an upgrade on Friday morning. And it did go smoothly, the upgrade to APEX 4.1 … until…
Until I started up the application, then I got this “Invalid Login Credentials:

This had me scratching my head for while… you can find out how I solved this issue by reading the full article on my blog.