BPs tend to go off food occasionally. I haven't had most of my BPs long, but someone of them are picky eaters. You just have to wait them out. Yeah it sucks when they don't eat because it means they aren't gaining weight, but you have to be patient. With the exception of my normal all my BPs are 2010s, and they are all rather small, my spider is the largest at 351g and one of my spotnoses is that smallest at 213.5g and she skipped her last meal.I don't plan on attempting to breed my 2010 until at least the winter of 2013, so I still have a ways to go and it doesn't bother me as much when they go off feed. The thing I'm learning with my BPs is that you have to be patient.
Snakes can fast for a while and still be healthy so don't worry about it too much.