Finally nailed this down. If you’re a big fan of using document properties in Windows Explorer to manage files, you may have found yourself frustrated by Visio in the past. On a Vista or Windows 7 64-bit computer, if you try to edit the document properties for a .vsd file (either in the properties dialog, or by editing in Explorer), you’ll get “Error 0x80004005: Unspecified Error.”
If you search the web, you’ll find a lot of people having this problem, a few half-hearted answers, but no real solution.
It looks like there’s a problem with the Visio interface on x64 Windows – this has been documented by the product team, and hopefully we’ll see a patch courtesy of Windows Update in the future. But for the time being, there’s no fix.