How did you carbonate the beer? (Pressure and duration if force carbed, amount and type of sugar if natural carb.) Also, how long did the beer ferment (ie any chance that fermentation wasn't done when you racked to the keg)?
Edit: also did you bleed the pressure off the keg when you changed the pressure on your regulator? The best thing I can recommend now is to go to the link below and click the "download the manual" link in the upper right. Read it, know it, love it.