oh well. sometimes they behave strange and in the end you know it's always you.
what i did:
i inserted the piece of code you mentioned (didn't know about redirecting STDERR this way, always used CGI::Carp qw(fatalsToBrowser) at the very top of the script. uploaded that thingy, reloaded the page and - oh well - there it goes. it displays sharply and clearly on my screen. everythings fine now. (well, not exactly: there are a few warnings in the log, but no problem with those they're easy to fix).

i do not have ANY clue what that piece of code may have changed so that it's working now and did not earlier. maybe one of you can explain?

thank you PodMaster for your help. it's always a pleasure to have a good teacher.

(and yes, i use DBI)