i have a guide on this that they refused to sticky... but try googling Adobe Flash Uninstaller and downloading that, and running it, it will completely uninstall earlier versions of Flash as there is sometimes an issue where the computer thinks it is fully updated but it missed a file somewhere and never catches it.
after that, open internet explorer and go to http://grandchase.ntreev.net and when it prompts you to install flash, let it.. this is what worked for me and a few others. its not a guaranteed solution, but its better than nothing