[Jimwth]

I'm not sure if I can be of help, but what have you already done with mayor, when you got the dagger? Did you get taxes for Dernholm? And if you did, how exactly did you do it? If you convince him to give the taxes to you before you end the dagger quest, I believe that you wouldn't be able to complete it. I may be wrong though, since I've played pretty long ago.