I had something like this happen before. I'm honestly not 100% sure on why my snake refused the rat, but not a single one of my snakes would take this rat. Maybe they knew something I didn't but I do know that it smelled a little odd (but not to the point that I didn't feel comfortable feeding it to my snakes)
It could have been a number of things, impossible to say for sure. Hopefully your next feeding will be successful.