It would be a good idea to double check the Windows Live ID associated to your main account. To do this simply review your account information via the dashboard (Account Management ----> Windows Live ID).
"Ok. I've check and they're the same!!! What now?" Right, no one account should be able to have the same Windows Live ID associated to them, however things can get a little muddled up some times and issues such as the one you're having can occur.
To fix this problem all you need to do is assign a new Windows Live ID to the account which you are signing into xbox.com. You will first need to recover the account, so do that first and then follow these steps:
- Sign into the account once it has been recovered.
- Hit the guide button on your controller.
- Scroll right, to the last page which is the "settings page".
- Select "Account Management" from the list of options.
- Select "Windows Live ID".
- Assign a new email address to the account.
Once this is complete come back to xbox.com and try to sign into your main account, things should now be resolved.
Troubleshooting support pages:
Recovering your xbox LIVE profile.
Manage a Windows Live ID.