One other theory that I have is that your Briquettes could have absorbed some moisture-that's a problem where I live with our humidity. I store mine indoors, and our grocery stores this time of year will have stacks of Kingsford out front. I won't buy a bag of charcoal that has been sitting outside, I like to think that I've fought my last battle with moisture-laden charcoal.
So, tell us how the baby backs came out!