Note that this is not what I get when I chose a wrong password (tried that on purpose) so that my log in data is correct. I can also log in with my adobe id on the adobe website without problems. Also tried to use the vendor ids from the ereaders with the respective passwords, but I get "Unexpected error", too.
I already contacted the adobe support but they told me that the would not offer support for this, since ADE was a free product. After pointing out that adobe does indeed make money off of it they simply replied "what has this to do with the consumer.". Way to go adobe, I made screenshot in case no one would believe that. Anyway, in case someone can help me I'd be very grateful. Otherwise: own what you pay for, stay away from DRM - it is just pure evil and bad software.