Some downloadable Xbox 360 games from Microsoft’s Games on Demand service aren’t compatible online with disc-based copies, greatly reducing the value of the downloads.

CrunchGear reports downloaded copies of online multiplayer-focused Rainbow Six Vegas 2 won’t let gamers play online with those playing with those using retail versions, and Joystiq says Lego Rock Band is suffering the same issues.

CrunchGear speculates the issue may have to do with how the games are named on Xbox Live:

Comparing our games revealed that his version is called TC’s Rainbow Six Vegas 2 while my version is titled RB6V2. Something must be wrong here. We have the same game but it shows up as we have different games. What’s going on?

The beauty of Xbox Live, particularly with downloadable games, is it’s possible for developers to fix bugs like this with patches. But before you download a game, it’s a good idea to Google it to see if anyone’s reporting fatal glitches.

Microsoft Selling Games On Demand With Compatibility Issues [CrunchGear via Joystiq]

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