What is this and how do you fix it? It usually happens when I'm fighting or getting quests.

People say this is a server error but i don't think so. It wants you to insert a disk into your disk drive. You don't have to do it to play, just keep playing. I think it's a promotional thing to make you buy their dbo disk.

Here is the disk you may buy: http://dbo.wasabii.com.tw/DB_Products/solid_01.shtml

99 Yuan? Thanks, btw. Helps a lot.

Yeah but, after a while, it keeps popping up, the game crashes.