Recently I upgraded from Ubuntu 20.04 to 21.04, and after the upgrade I could not access one of my Windows NTFS drives. The error message is:
gdbus.error:org.freedesktop.policykit1.error.failed:unix process subject does not have uid set.
Other NTFS drives open, but this one gives an error.
>Solution :
Exact same problem here – couldn’t access the drive via "Files" (Nautilus), with same error message.
It appeared to be mounted, though. So I copied the files I needed via the terminal.
After that the Disk showed up normally, also after unmounting/mounting it.