ok i found what had happened...
first, the "via" protocol was still enabled for the server connection; seems that this leads to problems frequently.
second, for some reasons two connection strings are listed in db.config - and the first, though not the second, held the correct connection data. seems that the first is used for testing and up to a certain point - whereas the second is used from then on.
anyway, the forum is up and running now.
thanks for reading this issue, and maybe this solution helps in future cases.
the thread can be closed now...