could be a corrupt DL, or a myriad of other issues.
best suggestion? DL the full game, uninstall the game, delete all files ie. the c:\program files\HTC folder (save the "settings" folder to a different directory) and reinstall the game fresh. put the settings folder back and all should be good to run.
you may want to remove any files in the setting folder with "video" in the file name to be safe.
good luck