Why is the downloadable Might & Magic: Heroes VI demo asking for a disc?

I just downloaded the Might & Magic: Heroes VI demo from Steam. On trying to start it, I'm receiving an error that suggests I'm missing a DVD:

There is no disk in the drive. [Cancel] [Try Again] [Continue]

All of the buttons make the dialog disappear for a fraction of a second, and then it appears again.

Has anyone else had this problem or managed to work around it?

Solution 1:

Oops, I just figured it out by going nuts on the dialog box.

Just hit Cancel 20 or 30 times - eventually it'll go away and the demo will start. Seems like a bad sign, but we'll see.