DAW playback all out of sync

[boborulz]

Hi,

I'm running Protools 7 (Mbox 2) with my virus Ti desktop (v3.0.3.00) and reason rewired into my session. I haven't be able to record smoothly yet, the Ti goes all out of snyc (especially if i use arps) i've got my buffer size set to 512, the ignore clicks and pops setting makes it worse also, have tried all sorts of different playback settings but i get a playback error when i change it (as i have audio running through rewire) and that same snycing problem to more or lesser degrees.. Also I will get a loud sudden crackling sound sometimes if i start the playback from a different spot...any thoughts?

Cheers