Lots of things can be placed under that description. Make sure you:
1: Have enough RAM to play Grand Fantasia
2: Check your email address to see if you have been suspended.
3:You may be lagging
4: You do a full scan/Manual Patch
5: You have every file you need to play Grand Fantasia. (This means if while you're updating, a certain file goes red saying "error", you may need to uninstall and reinstall game.)