der:hans, if you have not completely tired of experimenting with what
should already be easy to use, try approaching the problem backwards. In
this case assume that somehow their software has already found a password
for you and this is all just a poor way to report the problem. If the
screen you are getting stuck on allows it, request a link to get your old
password or a link to create a new one. This might clear out any garbage
associated with you account, especially stuff that may be hard to see.
Just a guess, but it sounds like you have thoroughly  tested all angles of
you current approach.

Misha
[resume cloak]
-- 

               KINDNESS

is most VALUABLE when it is GIVEN AWAY for

                   FREE