first of all, many thanks for the fast replies. You've been right, we
had a corrupted Recovery Log.
We've opened a PMR with IBM service and had to make this decision:
A) Restore the DB (Point in Time)
B) Do a DUMPDB, FORMATLOAD, LOADDB, AUDITDB
A) is painful regarding data-loss, B) is painful regarding time-loss.
We've decided to go for B), the first 3 steps used 1/2 day, let's see
how AUDITDB performs.
I hope this all will fix our problem, but I have no idea what could
have caused the problem...