Is it the dining buffet?
If you revised the start price of the auction but left the Buy It now price as is, or changed it, that could be causing the error (although the Buy It Now price isn't a reserve).
If there is a BIN price, the auction start price has to be at least 30% lower than the Buy It Now price, so if it is still $50 BIN, then the start price needs to be $35 or less.