If you are getting this issue when logging in you may not have a proper configuration file for our server. To resolve the issue you will need to go to your install directory for Dragon's Prophet and modify the client.ini to have one of the following options:

Ip=server.dragonsprophet.online
Ip=dp.adept.llc

If you get this error after getting a disconnect from the server, chances are you will need to restart your computer. This has mostly seemed to resolve the issue, so it may be a caching issue in the client, your computer, or just a network configuration issue between you and the ISP.