Alright, it seems we have two different problems going on with errors upon login:
500 - internal server error
This is the issue we have now been able to fix, and which does no longer occur. In this case, you would receive an error message like this:
Server Error
This error appears in the
loading bar, and is
not a pop up like the error above. This is a
different error. If you encounter this, please write a message to our
Support. We'll do our best to assist you there: we have found a way to at least temporarily fix this issue in most cases. We are still looking into what causes this issue, and we hope to find the cause soon.