Sometimes they just decide to be that way. I've got a pastel enchi doing that to me right now, following the rat and everything but just not taking it. Eventually she'll get hungry again, and eat the darn rat. I'll offer every week until she does. She's also getting close to 1000 grams, and most animals I've had seem to take a bit of a break around that time.

As long as your animal isn't losing weight, I wouldn't be too worried about it.