A few gamers who purchased Command and Conquer Red Alert 3 encountered a problem with their installs—EA had misprinted some of the serial numbers needed for activation. While the necessary code was 20 characters long, they'd only printed 19-character codes.
No biggie. The logical solution is that EA supplies customers with new codes, which they're happy to do if you're willing to photograph your serial and email it in. Otherwise, they've offered the public what must be one of the saddest "workarounds" in DRM history:
There is currently a work around that may allow you to bypass this issue. Since you have the first 19 characters of the code already, you can basically try "guessing" the last character. To do this, simply enter your existing code, and then for the last character, try the letters A-Z, and then the numbers 0-9. You should eventually get the right combination, and be able to play the game.
In other words, try all 36 possible combinations and you'll get there soon enough. If you've been shorted the complete serial number, we'd recommend guessing all 1.33674945 × 10^31 combinations.[EA]