I've deleted the .dat file. And patched. Still error occur.
I've noticed that when I patch, the .dat file comes out.
So what will I do?

Please do patch all to avoid sprite problems.. If you still encounter problems about the sprites you need to download New RO Client that supports Third Job..

this is where we get the latest RO Client:

http://www.playragnarok.com/downloads/clientdownload.aspx

After you have downloaded and installed, Update Valkyrie.exe, Ragnarok.exe & Renewal.exe

Then Patch our Latest Mini-Patch:

Download Option 1: megaupload.com megaupload.com14J4HH8H
Download Option 2: http://www.mediafire.com/?ws9a82lqe0gg558
Download Option 3: http://www.filefront.com/17652102/ClashRO-v3.0-Mini-Installer.exe/

Just Choose one of those three and install it on your RO installation folder, after finishing the install, Click " Clash Ragnarok Online.exe " and let it patch to the latest!

and your Done!