Why is it when you play xbox 360 games on the Xbox one it requires you to sign in when it...

To play games, even on Xbox 360, it has been required that you're signed into an Xbox Live profile (aka Microsoft Account). It's possible that previously it was configured to automatically sign in, and you didn't realize. It's possible that the account
that had auto-signed in removed the device from their account or changed security settings, and would require reauthorization to sign in.

Now, that is speculation on what might have happened as to why you're seeing a sign in screen unexpectedly. But the point would be that previously when using the 360, there was an account/profile being used.

This page here has details on how to add a profile to your Xbox 360. That would be for if there isn't
one present. Do you see if there is a profile already on there?

"You can get two free Xbox One games every month through Games with Gold, directly from your Xbox 360 or on Xbox.com. Build your game library every month and have games waiting for you when you move to Xbox One."
These are the exact words that are used when you sign up for gold. It leads you to believe that you can play downloaded Xbox One games on your 360. Otherwise why would somebody even bother. This is also happening to me and I'm very angry about it cuz I feel
like it's misleading.

When you signed in with your account on the xbox one did it show the same gamertag as you were using on the xbox 360.

Did you ever buy gold for your 360 before you started this?

Did you ever get online with your 360 and play Multiplayer games prior to this?

Before you started this endeavor had you ever signed into your 360 with an email and password previously?

This very well could be what happened:

The 360s had it where you could have what they called an offline profile where you did not have to have the live (not gold) just live service to play the games and all the game saves were stored locally.

With the One it is required to have a MS account and a live account (not necessarily gold) to even play the games.

Now if this is the case. When you signed in with your email and password on the one if you had never signed into anything Xbox (Xbox.com or a Xbox console) you would never have been given a gamer tag and would have either been given a choice to choose your
own gamertag or given a randomly generated system gamertag that you could change for free.

Now if you decided to make that gamertag the Offline gamertag that you had on the 360 and then went and downloaded your xbox one online profile to the 360 it would not have made that offline profile into an online profile it probably would have done exactly
what it did was put the new profile onto the system and put your old offline profile possibly in limbo.

This is why one of my fellow ambassadors asked when you go to the social tab on the 360 and it shows the different profiles on the console does it show more then one or does it just show the one that you just downloaded to the console?

When you buy a game, it's yours to keep forever. Free games do have some requirements. Xbox One Games With Gold titles require that you maintain your subscription to keep playing them (unless you buy it). Xbox 360 Games With Gold games, however, are yours
to keep forever.

And here a food for thought. Why is it that when you play classic Xbox games on the 360 why it saves to the hard drive with a added patch BUT you cannot do the same thing with 360 games on the Xbox one or Xbox one x, why not just have a simple extra patch
that allows you to save games to the hard drive of your new console?