I can't login to xbox pc live using my email. I've tried using my sons account and it went in.

Hi. My name is Brilliant, an independent advisor, happy to assist you today.

Can you try the forgot password option. Change your password and see if you'll be able to access it then.

SAME SITUATION

I created a XBOX LIVE account for my son over a decade ago. I used my work email address when I created the gamertag. Back then Microsoft's services were not lumped under one login (that didn't even exist). When Microsoft deployed their one login system they
merged my son's Xbox Live account into my work Microsoft account.

Now my son is an adult. We need to transfer HIS Xbox Live gamertag to HIS Microsoft account.

This is idiotic.

Using a @Outlook or other public domain emails is a terrible idea. I just tried it, and an email address composed of <companyname>xbox with @outlook.com apparently cannot be used. I've tried variations and they're all either taken or are being blocked... So... real nice job there! I can't use my domain and I can't NOT use my domain unless I create a really bogus name for the Live account.

Well done! /s

EDIT: Apparently "xbox" is banned completely in @outlook emails. So creating a targetted company email FOR AN XBOX using that is... impossible. Again, well done Microsoft! /s

EDIT 2:
THIS DOESN'T WORK! I CAN add a company email as an alternate login method, BUT IT DOESN'T WORK. Attempting to log in using it on the xbox.com portal causes the login screen to change to the company-specific login which attempt to create an Xbox account directly under the company email.

To clarify a little bit....

The email I had used when I initially created my XBox Live account is the same email as the one I started a NEW Gamertag to play GTA4 PC with. I can login with my email to Windows Live, but not to XBox. When I login to Windows Live, my old XBox account
with many games and 2000+ achievements is unavailable and in its place is the single GTA4 account.

it allows me to login on my original account, but it also gives the option to log into my account using a different email address that is not mine. I receive this code whenever I try to use a Microsoft application. I've tried looking for this other email on settings, but I can't find it anywhere as either an alias or some other account.