E-0101/E-0110: check your connection and whether websites load.
E-0102: data may be blocked or corrupted in transit. Switch from guest Wi-Fi to a home network without a login page, disable proxy, or temporarily pause antivirus HTTPS scanning.
E-0124: verify game files in Steam.
E-0201: check your connection and restart the game.
E-0301/E-0302: close the game, restart Steam and update the game.
E-0303/E-0304: wait 10–15 minutes, disable proxy, verify files and update the game.
E-0401: confirm Steam is online and using the correct account; restart Steam and the game.
E-0403/E-0404: verify files, add the game to antivirus exceptions and restart the PC.
E-0405: check antivirus quarantine, open Steam, verify files and launch from your library.
E-0501/E-0502: launch only through Steam, verify files and restart the PC.
E-0601: connect a physical keyboard and mouse directly before launch and avoid remote sessions.
E-0904: restart the game; if it persists, copy the error text and send it to support.