not sure what is going on. I hope it isnt true It is for my site www. mosaicmercantile .com one of the terms is mosaic tile. is this a keyword tracker issue?
Try updating again (a couple of times it might come back), I've seen it too. It is possible you've dropped on the datacenter that the API uses.
Also make sure you dont run out of API, it may only be used a 1000 times a day. When you run out, the keyword tracker shows N/A The next day you see normal results again.