The issue can’t be the same as the underlying issue was fixed already, but we’ll need logs to see why it’s failing.
You’ll need to enable ((trace logging)) in the config file (C:\ProgramData\NzbDrone\config.xml) and set the log level line to <LogLevel>Trace</LogLevel> you could also disable Authentication (<AuthenticationMethod>None</AuthenticationMethod>) to get Sonarr to allow you in without authenticating.