thanks for the reply
that's enough for me, at least so far
as i said, even if you say "sorry, there is nothing to say", that's much much better than not saying anything
if there is any way to help i'd gladly help. What i tend to do in these cases (bugs i can't reproduce for the sake of my life) is making debugging versions which write more information into the log file and send that to the customer with the problem. he sends me the logfile so i can narrow down the cause, i increase the log file information in that area and send the customer the next version. in the end i manage to pinpoint the exact line of code which causes the problem (especially for crashes) which then usually leads to a solution to the problem.
i know this is an annoying way to find the problem, but sometimes it's the only way i can think of, and it works.