So this is pain right behind the kneecap? If so, it might be chrondomalacia. I'd stop the leg curls for sure. I'd quit all lifting unless I had a qualified physical therapist show me particular exercises that she thought would help. Pain behind the kneecap usually means "raise your saddle." You can raise it as high as having about a 4mm gap below your heel with the leg completely straight. Try that and just do easy spins on the rollers or trainer for a couple of weeks.
There's a starter article on bike fit and knee pain here:
http://www.ultracycling.com/equipment/bikefit.html