Cannot add a product to My Support Profile: "serial number is associated to another Apple ID" I am trying to add the iMac I bought in 2011 to "My Support Profile".

So I copied the serial number from the "About this Mac" window, but when I entered it, I got this message:



I never had another Apple ID.

How do I prove Apple this computer is actually really my computer?

This problem is really annoying, and because of the same issue I have only been able to add 2 devices out of 8 that I own...

EDIT: As of October 2016; the URL seems to have moved here for the list of devices paired with your Apple ID. And it seems that the question is also now obsolete since only devices that a user can log into (such as devices with iOS, macOS or tvOS) can be added, so no more iPods.
If you have a proof of purchase or a receipt, Apple support will likely be help you correct this. Without these, they may question whether or not you own the computer.