One thing to check if you're trying to use Calibre across a network share. Make sure that you have mapped the drive from both your user logon and elevated. I do this from each of two command line windows, one regular and one as administrator. (The windows I use are actually PowerShell, but a cmd window will be the same for this.) Type:
Code:
Net use K: \\server\share
At each cmd window, where server and share are replaced by the win7 computer and the share name. And you can use whatever drive letter you want, but K: seemed right to me.
Something that Calibre is doing seems to need that administrative connection.