not enough rights to write to mag0

Can you manually connect to the path using start - run (keyboard shortcut win+R)? If running conquest as a service, does whatever user it runs as have access to the path? I think a generic user named "SYSTEM" is the user by default, but you can change the user the service runs under from start/run services.msc

"Everyone" in windows terms generally means anyone with a valid account on a trusted authentication source (usually only itself unless part of a domain) so users still need to authenticate to be included as part of "Everyone"