There's another possibility: even though you added corn sugar it might not have actually made it into the bottles.
I've had that problem with my last two batches: I added a corn sugar solution and racked the beer on top of it, expecting that to agitate it enough to mix. Apparently it didn't. One batch was poorly carbonated nearly throughout, and another batch had two bottle bombs and the rest poorly carbonated. I suspect not stirring left all the sugar at the bottom, so there was nothing for the yeast to eat.
I ended up uncapping them and adding 1/4tsp corn sugar directly to each bottle (previous experiments showed this to be the best amount for the carbonation I had). If you decide to go this route, be cautious: you may have a few dangerously carbonated beers, and by adding additional sugar you could create a risk of bottle bombs if any of the beers are actually well-carbed.
Lines on Ale
NB Irish Red; 1-gallon SMaSH IPA's: Citra, Cascade, Simcoe, Falconer's Flight and Mosaic; Bavarian Hefeweisen; Centennial Blonde; EdWort's apfelweinConditioning: Primary:
Mosaic IPAOn Deck:
Cherry MelomelGone But Not Forgotten:
Blue Schoon (Blue Moon clone)