snap not snaping to grid

hi there just moved to a i-mac 27’ 4g running cubase 5.3 and every things fine to start but once my track gets going the grid snap puts audio and midi events a few mm awawy from the grid you dont notice unless you zoom in …not sure but think it happens when i run a few sylenth 's…anyone having the same problem or know how to sort it …thanks

Did you make sure you have the grid type set to grid? There are other settings like “grid relative” that will snap to a relative position instead of right on the beat.

Are you absolutely sure you are using v5? This was a bug in v4, but it was solved with v5.