To avoid requesting players to log in every time when they play the game, their account data is typically stored in the game client after the initial successful login for a certain time (defined as a valid session). However, due to bugs or unexpected data corruption, players may sometimes be unable to log in properly.

A helpful first step in resolving such issues is to clear the cache on your computer, then log into the game client again.

For Windows users, find and delete player data under this folder %AppData%\LocalLow\MoonGaming

For Mac users, find and delete player data under this folder ~/Library/Application Support/com.medievalempires