The rapper was booked into Manatee County Jail Wednesday on two counts of possession of a firearm by a convicted felon -- and he posed for a mug shot on his way in. The exact circumstances that led to RW's bust are still unclear at this point.

In any case -- his attorneys, Bradford Cohen and Mark Rankin, tell us ... "The officers that made the arrest are incorrect. He is not a convicted felon and has never been a convicted felon. We would have hoped additional research would have been done prior to them filing these charges."

They add, "As with any case we will hold those parties that made the error accountable for their actions." We're told Rod has since been released on his own recognizance -- however, according to jail records ... Rod is still being listed as in custody as of this writing.

Rod has had some legal trouble before ... a couple years back, he was facing a DV case in Florida as well -- but in the end, prosecutors dropped the battery charges against him.