It's a huge win for the singer, who got arrested last year after the altercation with a photog in a Tampa nightclub called AJA Channelside. We got some video of the alleged incident, but the State's Attorney's Office tells us, "After a thorough review of the facts and information from the alleged victim, our office determined there was insufficient evidence to prosecute."

More specifically, sources with knowledge of the case tell TMZ ... the photog "lacked credibility."

In case you need a refresher, Chris was booked to appear at the club, and according to club management ... Chis and co. were pissed the photog was snapping pics of them when they'd already tried shutting him down and refused any photos. Apparently, the guy kept at it while Chris was in a DJ booth, and CB allegedly lost it.

The photog says Chris socked him in the mouth, and caused some gnarly injuries. Chris was able to leave that night uncuffed, but about a year later ... he was nabbed by cops on an open warrant for his arrest when he returned to the Sunshine State.

As we reported, officers were waiting in the wings at Chris' concert in West Palm Beach last year, and after he was done performing ... they took him in to the station, where he posed for this mug shot. He was released shortly afterward on $2,000 bond.

Chris has gotta be happy about this -- considering he's still got an open rape investigation going on in France. He has not been charged there.