The Sears in-store pickup system is flawed.
At each Sears store, there is a computer system that lists the number of items in stock. It is this system that you are accessing when you see on your computer that an item is available for pickup at your local store. The problem is that this system is not always accurate.
Let's say the item you ordered is a hand mixer. When you order it for instore pickup, the computer is told that there are three in stock, so your order is put through and you receive an order confirmation, without anyone physically checking that there is an actual hand mixer available for sale.
The computer system says your local store has three hand mixers in stock. One of these is the display mixer, which may or may not have the box, instructions, and all the pieces, and may or may not actually work. The department manager is technically suppossed to go through and delete all the display items from the computer system (changing the in stock total to two), but in practice, this rarely gets done, especially around Christmas.
So one of the mixers isn't really available. Now, your local Sears store has a problem with retail theft, as many stores do. Let's say that at some point one of the hand mixers was stolen. The person who stole it shoved the entire box under their coat and walked out. They were not caught, and since there is no empty package left behind, there is no evidence of the theft. If the box had been left behind, an employee could update the computer system, but most thieves aren't considerate enough for that.
So now two of the mixers aren't available. Now, let's say that the employee working in the hand mixers area is very kind and helpful to customers. About an hour before you placed your order, a woman doing her Christmas shopping picked up the last hand mixer on the shelf. Knowing that she had a lot of shopping left to do, the customer requested that the employee hold the product for her until she came back after lunch. The employee, wanting to provide good service, said "Sure!" and placed the item behind the register with the customer's name on it. Now there are no available hand mixers.
So, at noon, you place your order and the computer reads that three items are available and sends you an order confirmation--despite the fact that, in reality, there are no hand mixers available.
Shortly after you place your order, an employee from Merchandise Pick-Up recieves a message from Sears Online on his handheld computer that the hand mixer has been ordered for pickup at the store. He looks on the shelf for the product and doesn't see it. He then looks in the warehouse for the product, and doesn't find it there either. He may even ask one of the stock people from that department if they can locate it. They can't find the hand mixers because, despite what the computer says, there are no hand mixers. The Merchandise Pick-Up employee eventually gives up, and clicks the "Unable to find product" button on his handheld computer, triggering the out-of-stock email you recieved.