You may find info from this article helpful.
Note: Removing a device from your Apple ID does not override the 90 day timer. The timer must complete 90 days from the day the device was associated before it can be associated to another Apple ID.
Thanks Dominic. I've seen this article but this isn't my problem. I need to know how to determine which Apple ID my MacBook Air is associated with. When I try to register it using my normal ID, it tells me that it's already registered with another ID. I don't know what that ID is. I have about 6 ID's that I've used over time and I thought I registered the MacBook Air with my current ID - all my other devices are registered with my current ID but not the MacBook Air for some reason. So, if I can plug the serial number into some Apple utility and see what the Apple ID is that's associated with it that would be perfect.
Thanks again for responding.