Did you remove and re-insert the crankshaft bolt?
If so, did you get it tightened down? And, did you put the steel guide behind the crank pulley on so that it's outer edge flares towards the block (assuming that you took it off then put it back on..)
Finally, do the teeth on the belt match the teeth on the pulley? This may sound stupid, but I recall somewhere in a Samurai Galaxy Far Far Away where someone actually found a timing belt with the right length but the wrong teeth! -- Square vs Round or its it the other way... Don't make me take my timing belt off!
Hope this helps!