I know DiPrete had some problems with bribery and some shady state contracts that he pleaded guilty to in the late 90's. I don't know for sure if it was known back when he was Governor, but that'd be my guess.
In a sort of funny turn of events, the man who beat him by 50 points (Sundlun) ended up losing his primary four years later.
The DiPrete affair is a very lengthy, complex, and interesting one. DiPrete's term ended, and Sundlun's term started with the near total collapse of Rhode Island's banking institutions. DiPrete wound up being Rhode Island's equivalent of a mob boss Governor.