Windows services are very unreliable with mapped network drives (Microsoft doesn’t support them).
If the UNC path is failing it sounds like there is security on the share and either it needs to allow the system running Sonarr to connect without credentials or you should not run the Windows service and instead run NzbDrone.exe through the startup folder (so it starts with the computer) and has a tray icon.
Ok, I’ve gone into task manager and killed the nzbdrone task. Then restarted Sonarr through the exe file and it looks like it’s recognising the mapped drive. Upon restart I’m back at square one. How can I stop running Sonarr as a windows service and just put Sonarr.exe in the startup folder?
You can either disable the service in the Service management console (through Control Panel) or uninstall it by running ServiceUninstall.exe in C:\ProgramData\NzbDrone\bin.
I uninstalled it by running ServiceUninstall.exe in C:\ProgramData\NzbDrone\bin as you said. I’ve put the nzbdrone.exe in startup and rebooted. Everything is working as it should. Thanks very much I really appreciate it!