The Windows Live ID you entered does not exist or your password is incorrect!!

Yeah, it won't let me sign in with my GT with the new WLID I moved it to. When I try and open the GFW Marketplace it tells me: "Can't sign in. The Windows Live ID or password you entered is not valid. Enter your information and sign in again. Code: 80048821"
And when I try in a game it tells me "The Windows Live ID you entered does not exist or your password is incorrect", to which I will state that I am not getting my credentials wrong, I am sure of this.

Somehow managed to get a GT for another WLID I have a while ago, and I can log into GFWL and GFW Marketplace just fine with that one.

sounds like you entered it wrong and the system thinking the misspelled email or incorrect password is a new windows live ID and created a new account based on it. you will have to contact support to get into your account using your original log in/password.

sounds like you entered it wrong and the system thinking the misspelled email or incorrect password is a new windows live ID and created a new account based on it. you will have to contact support to get into your account using your original log in/password
good luck.

You have to have the password for the windows live id you need to change.

On the console > Sign in > Acount Management > Your Information > Windows Live Id > Change Live ID > Enter password > Enter new email and password.

Online, if not hotmail or live.com > account.live.com > sign in > Windows Live id: (your id) > Change.

I looked this up on xbox.com/support, hope this helps:

Error: Email address or password is not valid (80151103, 8015D000)

Windows Live ID problem

This article speaks to what to do if you get an error message when you try to do one these things:

•Sign in on your console or Xbox.com

•Change the Windows Live ID associated with your Xbox LIVE account

•Create an Xbox LIVE account

These are the error messages you might see:

The e-mail address or password you entered is not valid. Please try again.

This profile cannot be downloaded right now. Status Code 80151103

This profile cannot be downloaded right now. Status Code 8015D000

Typically, this problem occurs if you entered the wrong Windows Live ID credentials (email address or password), or if there is an issue with your Windows Live ID.

Things to try

Solutions

Solution 1: Make sure that you are using the right Windows Live ID

Solution 2: Check your Windows Live ID on Xbox.com

Solution 3: For a child’s account, use the child's Windows Live ID

Solution 4: Reset your Windows Live password

Solution 5: Contact Windows Live support

Solution 1: Make sure that you are using the right Windows Live ID

If you have more than one Windows Live ID, make sure that you use the right one — the one that was used to create your Xbox LIVE account. If you forgot, see Manage your Windows Live ID.

Note If the Xbox LIVE account is a child account, make sure that you enter the child's Windows Live ID.

Solution 2: Check your Windows Live ID on Xbox.com

To make sure the Windows Live ID you are using is the right one, try signing in to Xbox.com by using the same Windows Live ID that you are trying to use on your console. If there’s a problem with that Windows Live ID, you are prompted to correct it.

If you are signed in to an incorrect gamertag or if you are prompted to create a new Windows Live ID, you are likely using the wrong Windows Live ID.

Solution 3: For a child’s account, use the child's Windows Live ID

If the Xbox LIVE account is a child account, make sure that you enter your child's Windows Live ID. You must use the Windows Live ID that was used to create the account.

If your child's Windows Live ID was automatically created as part of Family Account setup and you try to reset the password, email is sent to the Windows Live ID parent account (the Xbox LIVE family primary account). Follow the instructions in that email
to reset the child account's password.

If you only want to download the account profile, use the Download Profile feature when you are signed in with the Xbox LIVE family primary account.

Solution 4: Reset your Windows Live password

If you can’t remember your Windows Live ID password, try resetting your Windows Live ID password.

Solution 5: Contact Windows Live support

If you can’t reset your Windows Live ID password, contact Windows Live support for help in recovering your password. Xbox Support can’t reset your Windows Live ID password for you.