Welcome to the forums.

Unfortunately the best you can hope for from Bethesda is a copy and paste Un-helpdesk type response probably advising you to start a new game.
Stick around on here and this community will try and help you, someone will have had your issue I'm sure.
The follower problem suggests you still have one assigned and he/she has gone missing, that's why you can't take another. I'll have a ferret around the forums to see if I can find anything as off the top of my head I can only think of trying an earlier savegame.