This message means that listing this item would cause you to exceed your seller limits for this particular month. There are ways to handle this issue. You could end some listings if possible, reduce quantity for some of the outstanding listings(because even if the item is one item with large quantities all of them count as an item. EX: item is a Radio, Quantity of 50=50 separate items) or a combination of both. You could change you Max Quantities to list as well to a smaller number, effectively keeping any quantity over the amount you specify in reserve. When you sell more of the item, the system will up the quantity on the item back to the number you've specified; this allows you to list more items.
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That number can be found in your SellerChamp eBay settings in the screenshot shown above.