Are you on Windows Vista, or Windows 7?
The following will work on both Vista and 7, although it addresses Vista. Please be sure to follow each step, even if it looks like something you've tried before. Vista and DEP can get picky, and sometimes will make you try it twice.
There are several security features in Vista that can interfere with a running application. The most likely cause of this problem is that Vista's Data Execution Prevention (DEP) is interfering with the digital rights management (DRM) software that handles the activation code that unlocks the game's full features.
DEP is an important security feature of Vista and should not be completely disabled; however you can disable DEP for individual applications when you encounter problems with the way Vista handles such applications. To read about what DEP does and how to change its settings, click Start on your Vista taskbar, then click Help and Support. In the "Search Help" field at the top of the help window, type "dep" and press the Enter key on your keyboard. You should see several entries related to DEP, which you can browse to become familiar with this Vista feature.
To change DEP settings, click on "Change Data Execution Prevention settings." Depending upon how Vista is set up on your computer, you may see that DEP is turned on for all programs. If this is the case, you can choose to either set DEP only for essential Windows programs and services, or to disable DEP for the game only by follow the instructions for turning off DEP for an individual program.
If that does not work, right click on the .exe file and select 'Run as Administrator'.
Let me know how that goes.
