CHRIS BROWN’s post-sentencing celebration this week has landed a Los Angeles nightclub in trouble – because he was partying underage.

The R&B star shocked fans on Tuesday (25Aug09) when he was snapped dancing in Hollywood club Guys & Dolls, just hours after he was handed a five year probation order, six months hard community labour and ordered to stay away from Rihanna, who he was convicted of assaulting.

A spokesperson confirmed on Friday (28Aug09) Brown’s actions breached his probation, because the 20 year old was in an over-21 venue.

And now the hotspot’s bosses are facing an investigation from Alcohol Beverage Contol, because they allowed an underage reveller in.

The ABC confirms to TMZ they are “looking into reports that are surfacing regarding an underage individual in Guys and Dolls”.

If proven, the club’s owners could lose their liquor license.