Stout carbonation

Ok, here's the issue...

I bottled a dry stout (Beamish clone) on December 13th. I added 2 g of corn sugar to 4 gallons 0f beer as recommended by tastybrew.com's priming calculator. I tested two in seven days and both were carbed perfectly. I tried another on Christmas Day and it was flat, completely, utterly and disappointingly flat. Chalked it up to bad mixing of sugar, low yeast count, bad luck, etc.

I tried two more last night. Both completely, utterly and disappointingly flat again. What could be the issue?

Just for more info, I always pour the priming sugar solution into the bottling bucket before racking the beer into it. That way the sugar can be thoroughly mixed as the beer flows in.

Should I just chill for 2-4 weeks or consider opening and re-priming?

yeah. as much as it may suck give it 2 more weeks before you really consider recarbing. I always give all my bottles a good shake after about a week or so just to make sure the yeast aren't sleeping in there

Yes, wait it out. 3 - 6 weeks works well for me: 3 weeks for pale ales, etc. and 4 to 6 weeks for stouts, porters, etc.

Make sure they're nice and warm too, 70F works best for carbing in my experiences...