wrong region

Make a new gamertag like Onxy said and use it to download things on, you will still be able to access the DLC with your main gamertag, unless there is a region lock on a specific piece of DLC such as the last
one for Black Ops.

Sorry, but some games are region locked and will not work in other regions, nothing can be done.

Also to add Romania is not even a supported Live region so you cannot buy Live for that region and you will always run into trouble when it comes to downloading anything from the marketplace sorry.

Yeah, unfortunately the discs are region locked. I tried using a Japanese copy with my PAL Xbox so I could use Kanji and had same issue. You'll need to import a US Xbox 360 to use your disc.

Hey Filip,

Thanks for reaching out to us today! I'd be happy to help.

Xbox 360 games are basically DVD's and are coded in two different formats based on the region you live in.

NTSC stands for National Television Standards Committee. PAL stands for
Phase Alternating Line. NTSC is the standard broadcast format in the United States, while PAL is the standard broadcast format in Europe, Australia, and parts of Asia.

If you got your Xbox 360 from the Czech Republic, then it may be that the used game you purchased is coded in the other format. You will need to get the discs from the same region you got your Xbox 360.

I would suggest you go back to the point of purchase to see if they can exchange it for you.

I hope that helps!