Hi, I've added in my basket "Return to Castle Wolfenstein", but when I go to check out, the system says:

Please note that The Elder Scrolls: Arena AND The Elder Scrolls: Chapter II - Daggerfall is included in Return to Castle Wolfenstein but you already own this item, and will not receive another copy when you buy this pack.

I don't own Return to Castle Wolfenstein, and I think this message is a system error. Can you please help me?
Thank you.

I don't know why you can't buy RTCW, but the message about The Elder Scrolls isn't a system error - why would it be? Also, it's a NOTE, not an "error message".

I think it's referring to the The Elder Scrolls: Arena and The Elder Scrolls: Chapter II - Daggerfall games. Check your game library.

Arena & Daggerfall are given for free if you buy a Bethesda game. Since RTCW is published by Bethesda, you are eligible for the two free games but the message shows you already own them (probably because you already purchased another Bethesda game in the past and received them for free then).

The message isn't saying that you already own Return To Castle Wolfenstein but rather that you've already received the two free games (Arena & Daggerfall) that come with it. Ignore the message, it's perfectly normal to see that when buying a 2nd (or more) Bethesda game.

Thank you, as you said, it was a only a Note. I bought the game successfully! Thank you, as you said, it was a only a Note. I bought the game successfully!