I don't know why it's happening, but I thought I'd pop in and say that you're not the only one who is getting this. It happens to me occasionally, with no explanation - the price IS valid, there are no typos like a comma instead of a period.
Completely clueless about why it happens as all of my listings are from "make similar" and have always worked (with valid prices) in the past.
Aucitva guys, what's up with this?