Thank you for your post.
From your description, I'm assuming "Check for Updates" is not grayed out as they are able to select it.
When "Check for Updates" is selected, a https: command is sent out, so is it possible the clients are behind a firewall of some sort? This would account for nothing happening.
Any other information you can provide may be helpful.
Right, "Check For Updates" is not grayed out.
But I probably wouldn't worry about this issue too much -- I only have one client who is reporting these problems. They have over 100 FileMaker users in their office, but this client always has tons of networking problems on their network, so I would assume it has something to do with their network.
However, one thing that is interesting to note is that this client believes that this problem has something to do with FileMaker Pro's preference entitled "Notify me when an update is available". They state that when this checkbox is unchecked, pulling down from the "Help" menu to "Check For Updates" doesn't work. But when that checkbox IS checked, then pulling down from the "Help" menu to "Check For Updates" DOES work.
Who knows. I wouldn't worry about it too much. It's probably some networking issue on their end.