Hey - This is Jason (littlebear) from the comments.
I'd like to clarify some behavior some users are seeing. In one of the comments I seen the user had Kaspersky and said ever since they installed it they could not install giveaways. I believe this behavior is only isolated to large file installs such as the one that GGOTD had served up today and one previous one that other users have been having trouble on. Otherwise is the file size is in the smaller triple digits or below, the virus scanner won't have a problem with the wrapper / copy protection embedded in the setup file.
Also, I've found during my tests that some programs such as AnyDVD, Alcohol 120% , Daemon Tools and other CD Emulation programs also interfere with the setup process as well. So exiting all these programs from the system tray before running the installer greatly minimizes the chance of the installer failing or getting the dreaded key decryption error.