Can't pair my son's 360 profile to the Xbox Live account I created online.

I had the same issue trying to setup convert my sons offline account to LIVE. Tried to "Join Xbox Live" from console, was told I needed to to live.com and create a Microsoft account. Went online, paid my $0.50 to verify. Went back to Xbox console and
tried to "Join Xbox Live" again. Entered my son's new child Microsoft account email address and password then entered my parental Microsoft account address/password and was received a notification that child Live profiles need to be created online at xbox.com.
As with you I went back to the computer and created the Live profile and it assigned his Gamertag. When I went back to the Xbox and tried to migrate the offline account to the Live account and was told that the Live account was already in use (or something
to the effect). So I had to create a NEW Xbox profile for my son. So now he has an offline profile with all his achievements and the new LIVE profile with nothing.

This makes no sense. There should be a way to connect the newly created Gamertag to his existing offline profile as you can with an adult profile.

I would like to convert my other son and daughter's offline accounts to LIVE but am not sure I want to go through the hassle and them have them lose all their achievements.

I'm having the same issue. My son has an xbox 360 with an offline profile. I'm trying to convert that to a live account. I tried signing up for the live account from the console and was unable to continue because of the age restriction. So I went online
and eventually figured out how to create a child live account (an unnecessarily cumbersome process). I then logged back into the console with my son's profile and tried to sign in to the live account. That just takes me back to the profiles screen. So I
logged into the profile again and tried to sign up for xbox live. I was able to complete the sign up process but received an error about the email address being associated with an existing account. So, does anyone know the exact steps I need to follow to
convert my under-13 son's offline profile to an xbox live profile. This really shouldn't be so difficult.

also...make sure your son has a Live account and not just a xbox 360 profile. Meaning...his account is downloadable via Xbox Live rather than just a profile on an xbox360 as most kids have.

The Xbox One will require you to create a"child" account as you can't just let your son use your profile because once he logs in somewhere else, it logs you out.

Also, there are financial and privacy reasons that this would not be recommended.

I got the same error code of 80154002 as well. I accidentally created a new xbox live account under the wrong profile on our xbox 360 instead of my profile, and, when I went to try and change the user account linked to the profile, I get this error message.
And I can't find anything online about it either.

Yes!!! I'm in the exact same boat, also!!! My son got an XBOX 360. We both created our local (offline) XBOX profiles and started playing offline. I was able to promote my profile to XBOX Live since I am an adult. When I try to promote his profile to XBOX
Live on the console, it tells me that I must create his account on the website. After I did that, I cannot link his local (offline) profile to his newly created XBOX Live profile.

Is there some type of answer where my son doesn't loose all saved game data?