I used to be a staple on the Deus Ex GameFaqs forum - in 8th grade, I bet Deus Ex 27 times. I also loved the sequel.
Now, as a senior in High School, I decided to play some old games and game across Revision. It seems great, but this error is a bummer.
I'm assuming its a D2D error as I tried it on several different (more powerful) computers and the same problem occurred. D2D requires an authorization code so it might be some sort of access code. Either way, I'll see how it works with the CD version.
Also, if the D2D download turns out to be the problem, you can include that warning on your download page for your final version.