Greetings Hannibal Smith, welcome to the forum

that probably means you aren't using all the factions in your descr_strat file - its fine to do that - but if you don't include a faction in that, you can't then use them as the faction creator in the descr_regions.txt file that's the third line down in the regions entry like
Tribus_Saxones
Bordesholm
germans
Saxones
232 41 55
timber, slaves, amber, dogs, pigs
5
3
check that file and make sure you aren't using anyone you don't have in strat....