Please try manual update first. If the problem persists, try uninstalling, as well as removing all the related files and restart your computer. After that you can reinstall by clicking client download at http://rowplayon.com/Page/en/download/download.jsp

Hello! Thank you for your reply.

This is what I meant by "clean installation". And still, the problem persists, this is why I asked here.

That problem/ error occurs when your client is not same as our client.
if you have uninstalled and delete the client/game and have turned off the PC to remove left data before reinstall. This problem should not occur.