https://forum.plutonium.pw/topic/9/common-issues-and-frequently-asked-questions-t6
This error occurs when you are trying to launch an outdated version of Plutonium. However, this should not happen if you are launching the game via Plutonium.exe which checks for updates on each launch. So if you are starting the launcher via plutonium-launcher-win32.exe please do not. Launch via plutonium.exe