Tom,
Unfortunately, the first link you provide does not link to a solution, nor does it link to any further information on this topic.I also found the contents of this link using this site's search function, but when I followed the contents I quickly discovered that it answers a different question and contains no information on this topic.
I'm using Windows 7 SP1, PGP Enterprise Desktop 10.1.1 (Build 10) (Not so helpfully, the open 'About PGP' dialogue box disappears when you try to type the version data text here...) Corporate. Global Directory does not find anything... So, yes, almost certainly a corporate network protection mechanism is my underlying problem.
But the second link that you provided: 'Use the web interface', solved the problem. Thanks!
Moral: Don't always rely on the provided menu functions!
Improvement opportunity: If there are a limited number of high probability causes, then the error box could usefully include a reference to them rather than merely stating: "The server key for the PGP Global Directory could not be obtained.". Something like: '"The server key for the PGP Global Directory could not be obtained. If you are trying to upload your public key, then you could try using the web interface directly: https://keyserver.pgp.com/vkd/GetWelcomeScreen.event If you are trying to <insert other high probability causes and their solutions>"