The Sims 3 Wont let me move to another house...why is this?

Hmm, I haven't come across this problem myself but are you able to click on edit town from the option menu? If so, you could try clicking on your household in edit town then "save copy to library" followed by "household only" this way you can save your Sim to the library but they keep their skills, money and things in their bagpack.

As for you chrisbluemonkey, have you tried the reset sim method? Don't know it off the top of my head but I think it's easy enough to search for on google or something.