As you know cityville inventory limit now changed and there’s an individual limit per item read cityville updates 3/9/11 for more information
full inventory /item
your inventory cannot hold any more of this item
and here’s the reason why zynga made this changes :
Recent Inventory and Energy Changes (3/9)
We’ve recently made a few changes in the way inventories work in CityVille. The items that are currently in your inventory will be unaffected, and nothing that you have earned will be taken from you.