Taken gamertag change

If you search for a gamertag and there's a profile for it, then it's still considered active. There are several people with that tag already. So you can use it, but you will be given a suffix to differentiate yourself from the others.

Already taken as Gamertag: B Lights. The system doesn't count spaces or capitals.

It can be used by a Zune subscriber, Bungie.net account holder, banned or in limbo (i.e. original XBOX account that has not been converted over to XBOX 360). It can be associated with an account in another country. Or the user's profile who owns that account
is configured to prevent any public view via xbox.com or other sites (zune, bungie, etc).

google "blights gamertag"

It's simply not available.

Here's a bit on GTs from
our guide:

I can't change my Gamertag (GT).

Just because you can't friend request a GT doesn't mean it is available. First of all, all GT are tied to services like Zune or Games for Windows LIVE. If a GT doesn't exist on Xbox, it might be in use on one of those services. Also, spaces and capitalization
are not considered when looking for available GTs. For example, "Major Nelson" is the same as "MajorNelson" is the same as "MaJoR nElSoN". Basically if the service says the GT isn't available, it isn't available.

I heard old GTs are being re-added. When will "This GT" be available?

There is no schedule or estimated dates for when certain GTs will become available again. GTs are not an on-demand service. They will be available when they are available.

It's taken without the space. If you try to change to a gamertag and the system says it is taken, it is taken.

https://live.xbox.com/en-US/Profile?gamertag=XeroShotz