Sorry for bumping old posts, but in case someone is using the search engine for solutions, the best thing that I can offer for those using Windows Vista and Windows 7 (whether it be x32 bit or x64 bit) is to go to your Grand Chase directory, locate main.exe and grandchase.exe, right click each application, go to Properties, and under the Compatibility Tab, be sure that to Check Mark the box called "Run as Administrator" to bypass the User Account Control settings.
If that doesn't work, then most likely it's a GameGuard related cause. Use an anti-virus scanner* and scan for viruses. Then, I would usually suggest others to turn OFF their anti-virus scanners and other security set ups (ie Firewalls, Windows Defender) and try running the game again.
* If you're using Norton, I suggest uninstalling it and install a better install a better anti-virus scanner. I suggest downloading avast! Home Edition if you want a free virus scanner.