I use Ktorrent 2.0.3. On some occasions I get the message "invalid answer" ("ungültige Antwort") in tracker status. Other people at the same time dpn't have any problems with the tracker, and even my other uploads using that tracker aren't affected.

What to do?

Upgrade to ktorrent 2.2.5. In case you're running Debian etch, see
http://ktorrent.org/forum/viewtopic.php?p=12607#12607 for upgrade instructions.