SeeleyOne, just to confirm - you didn't reinstall Hero Lab after updating to Windows 8.1, correct? You just started Hero Lab after updating and it told you that you had to reactivate?
Edit: Also, both of you updated from Windows 8, correct? Not an earlier version of Windows?
My naughty brother edited my post a bit more that I realized. I typed one, and handed it over to him to make sure that I said what he wanted it to say, and he sounds a bit more frustrated than I was.
Of course, it was his computer that it was on, so that might explain it.

He upgraded to the more recent Windows 8 version this last week, Tuesday or Thursday or whatever day it was. We get to his house to game and two of the players had not printed out their characters. He tried to run Hero Lab and it would not work.
I am thinking that the license is too new, as it was a third license that I bought so that we can use it at his house (we get two at start, and can buy two more). I have it on two machines at my house, but both are desktops (mine and The Kids computer, which both still run Windows 7). I think that I bought that new license on the 21st or so of last month.
The new Windows 8 update screwed with several things on his computer, Hero Lab was just one of them. It was an annoying time to find that out. Personally to me Windows 8 appears to be a downgrade, not an upgrade.
I handle most of the updates at my house, and then we use his while gaming at his house. In most cases this would not really be an issue, but it was just a factor of timing (and Windows 8 being infamously stupid again).