but I think it should be lib, not usr/lib (which doesn't exist).
(If you want to test that, download http://rox4debian.berlios.de/0install/Tasklist.xml, edit it as above, and drag your edited file to AddApp. You won't get automatic updates to Tasklist this way, of course, but it will let you see if that's the problem.)
Tasklib / libwnck
Tasklib's feed does:
but I think it should be lib, not usr/lib (which doesn't exist).
(If you want to test that, download http://rox4debian.berlios.de/0install/Tasklist.xml, edit it as above, and drag your edited file to AddApp. You won't get automatic updates to Tasklist this way, of course, but it will let you see if that's the problem.)