Where does this error message appear? Right after entering your login information, after character select, or in-game?
If it's after entering your login information, then try reinstalling. I'm almost certain that you took the process of moving Amistr's files to your Ragray/Sakray folder manually, instead of installing it to either of those folders or moving Ragray/Sakray to your Amistr folder.
It really isn't recommended to do any moving manually unless it is Ragray/Sakray that is being moved manually.