This indicates that the MapleStory client was not installed properly. The error should go away if you uninstall then reinstall the MapleStory client.
MapleStory Uninstallation (Use one of the methods below)
- Start → Control Panel → Add/remove program (or Programs and Features depending on your OS) → Uninstall MapleStory
- Start → My Computer → C Drive → Nexon Folder → Remove the MapleStory folder and remove the MapleStory shortcut from your desktop