I have a 2008 R2 server with a 40gb C: drive that showed as having 24k free. If i unhide everything and then use diskmonger or disktree then they report that only 24GB are actually used.
Shadow copy isn't enabled, there are no previous versions of shadows stored.
I've see this question come up lots on various forums, but I'm yet to find an answer from Microsoft.
I look forward to hearing back from someone with the fix!
Regards
Hunter