Reply to Loosing bpm

I just started having this problem . I am playing a set and anywhere between an hour or 2 ,in one of the decks my bpm will go away. My tempo fader does not work I loose all control over tempo .No matter what i try it doesnt come back , it slows down and goes out of sync with my mix (happens alot when i start blending 2 tracks together for the mix). I hit sync ,offset ,shift, nothing works untill I load the next track . It is screwing up my mixes . I am running mac 2.53 4gig ram 250 hard drive with external tb drive just has music on it . tp2 s4 .Any help would be greatly appreciated . if you need mor info just ask
Thanks