I guess it could be that your frequency settings might be out of date, are you using the latest version of kaffeine?
Two things you could try:
1. Backup all the entries in ~/.kde/share/apps/kaffeine/dvb-t then empty that directory. When you try and use dvb kaffeine should try and download the latest frequency lists for you, that's if it can't find any lists in other of the places it looks
2. Or download http://hftom.free.fr/kaxtv/dvbdata.tar.gz
this list and extract it in the above named directory and rescan.