No, that's the unallocated space, not free disk space. It's disk 0 that it tries to run Winsat against, though I do wonder if it is indeed trying to run it on disk 0 or something else.
It would be useful for you to download, extract, and then run
process monitor, then run the
winsat disk -v command as before, wait for it to fail as your screenshot shows of the result of the winsat disk -v command, and then save the process monitor log (file > save as, all events) and then compress (Zip or RAR) the resulting .pml log file and upload it somewhere for us to take a look at.