whenever i try to join my friend it says " Version mismatch, please restart to sync your version, also tell the person you were trying to join to do the same "

I have played with him before, but this is new, how to resolve this issue???

I kinda doubt it but do both of your copies match ie same region, it may help...

And did you try actually shutting down both your ps3s?

no, the copies are different regions, he has a region 2 copy while i have a region 1 copy, although if the regions actually mattered, we would have never been able to play in the first place, we have played quite a couple of matches together before.