AuctionCut

Greetings,

I recently sold an item and after 7 days, I had not received payment. I sent 2 invoices during this period, but received no response. On the 8th day I submitted an Unpaid Item Dispute because all my efforts to contact the buyer resulted in a message saying "The form is not available at this time.
You are attempting to communicate about an invalid item."

Does this mean the buyer is no longer registered? Or an issue with the transaction? If so, do I need to continue with the UID process?