If it's leaking in the neighborhood around the quick disconnect (I assume that's what you mean by "connector") and it's only leaking when the quick disconnect is attached to the keg, it is almost certainly the liquid post o-ring. Get a new one and grab some keg lube also, put a very thin layer on there before you slide the QD down.
Other possibilities include:
Leaky QD: make sure the internal o-ring is in place and the top is tightened down. It's rare for them to leak from the factory but not unheard of. If it seems to be leaking out the bottom of the QD, it's probably not this.
Bad connection to QD: make sure your tubing is sound and a clamp is firmly in place. If you have flare fittings, make sure you went hand tight then just barely snugged it with a 9/16" wrench. Overtightening the MFLs can make the plastic crack pretty easily.
You should be able to narrow it down based on where the beer trail originates from. For now, pop off the QD and make sure the leak isn't still there.