The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
Caused by: java.nio.file.NoSuchFileException: C:\Users\L****P****
Something is probably blocking the file
Disable any security software
if it does not work:
You can try a different client; https://github.com/Eternal-ll/Ethereal-FAF-Client/releases/tag/v0.5-beta-fixes
