Changing MAC address only works with some addresses

This is so strange. I was trying to change my MAC address to D15EA5EDB020 but it wasn't working. I tried many methods. Then I tried changing it to other things, and sometimes it works and sometimes it doesn't. I'm using the built in Intel WiFi Link 5100 AGN card on my laptop, and am doing the changing with Technitium MAC Address Changer, but I've tried other programs and doing it manually through the registry with the same results. I made a list of the ones I tried and whether they work or not. Y means it works, N means it doesn't. I can go back and try them again and get the same result.
It seems so strange that some work and some don't. I'm not sure if it is a problem with Vista, or the network adapter. And I can't seem to find a pattern of which ones work.
When it doesn't work, it displays the default MAC (00216B0E27E2).

Question, why do you want to change the MAC address on your pc?

To be funny, and for anonymity.

I wouldn't mess around with Mac addresses unless you Know what you are doing because you can mess up your Computers IP address and the Mac address

Best Regards,
Josh

I can offer clarification as to why some of those new MAC addresses worked while others didn't. The first octet (first pair of numbers) has to end in binary xx10 or in 2,6,A,E.

There isn't enough space on this forum for my banal explanation of HEX to Binary translations and others do a better job of describing it than I could.

The binary rule especially applies to WiFi adapters in Vista, Windows 7, even WindowsXP. Traditional CAT5 adapters are more flexible and likely would've accepted all of your MAC address combinations.

Spare me the criticisms and innuendos of illegality when changing MAC addresses. The reasons are varied and legitimate and if for no other reason than the purpose of seeking knowledge. Anyone who openly questions and criticizes the reasons why without learning why are just as addle as they are feeble.

HTH