If your having problems, i would drop either BZNeil or BZThomas a pm or call them at BZ Paintball supplies on 01642 605000, they are Tippman dealers for the uk, all qualified Tippman techs and really know there stuff they will defianlty be able to help you out.
Try and have as much information to hand as possible and if possible try and find out what paint you were using as this does sound the most likely case to me but I only got my hands on a load of tippmans last week for the first time (off BZ) and they all worked great with site paint. These guys know there stuff.
Hope this helps
Jon