XBox 360 backwards compatible?

I have 2 Xbox 360 Slim consoles, one of which can play Xbox and the other can't. Both disk and download games were tested. One can play the backwards compatible games without problems while the other always gives an error. Does anyone know why this is and whether something can be done there?

Then the Xbox that does not play the Xbox Classic title does not have an original hard drive.

Unfortunately, you can't use the downward compatibility only with original hard disks

Both have to be updated to the latest version, both consoles need an original hard drive which must be inserted around the slim console below. The 4GB internal memory (which not every 360 slim has) and external memory can't be used as a replacement; an official hard disk must be purchased.

When all of this is safe for you, connect the console to the Internet and then start the game. The console then downloads data for the xbox classic emulator (for the best sake I don't know why this is not already implemented in the latest 360 software)

If that doesn't help, write to Microsoft's https://support.xbox.com/...contact-us.

One hard drive is apparently original and the other is not. Good to know. I really don't understand why Microsoft has never released the emulator otherwise. It could have been done really well with an update. But thanks for the answer ^^