In mass does a dually pickup need to be registered commercially?

i live in massachusetts and drive a dually pickup registered with passenger plates. i have owned this truck since august of 2009 and have driven and gotten it inspected without any issues. a few days ago i received information from a state trooper stating that my truck is registered illegally and requires commercial registration, something i was never aware of and threatened me with fines. is the trooper correct, or was i simply getting hassled by the trooper, as i stated i received the plates legally from the rmv, re-registered it without issue, passed inspection in 2009&2010 and have driven it without any sort of issue. any help is greatly appreciated