Many times the condition of an item isn't acceptable to eBay for the category you've chosen to put it in. There are many items in fact that must be sold Brand New; Example: Food, drugs etc.
Above is a diagram of acceptable conditions and how they map to eBay. Very soon, we will pull eBay conditions directly; but the rules as to what can be listed in what condition will not change.
In addition, the item could be in the wrong category and will need to be manually moved to the correct one.
Categories are chosen by reading the first three words of the title. While they usually go correctly, sometimes they need to be modified.