audio distorsion and clipping on cubase 6.5

why after update to 6.5 cubase start to play distorsion…it seem a problem of audio buffer but sound card work fine…i try to export all my project,sound good but after a bit sound goes in clipping and distorsion…sound bad…i see a cubase artist 6.5 update…is valid for cubase 6 ???

Edit

Was a microtonic in a instrument track…

close it!