Playit.gg does not officially host old versions, but the file is archived on some third-party repositories (use extreme caution with checksums). The official SHA-256 for playit-0.9.3-signed.exe (if ever released) is not publicly listed, so always verify via any available signature.
Another instance of Playit is running, or the local port is occupied. Fix: Check Task Manager for other playit-*.exe processes. Change the local port in your game/server config. playit-0.9.3-signed.exe