Wasn't just UK users, but several others around the world. Looks like some people in Germany and Switzerland also had this issue.
It affected all users that had their regional settings set to a country that has a certain language, but it's not the "original" country that language comes from. So, for example, German (Switzerland) had the problem, but German (Germany) didn't, Italian (Switzerland) had the problem, but Italian (Italy) didn't.
The real reason it's what looks like a Windows bug: those countries all use the 24 hours time format, but Windows incorrectly sets the AM/PM postfix to the hour format, which is wrong if a country uses the 24 hours format, and this likely confused some part of the code that checks the time, most likely not even in our own code, but in the 3rd party library that handles online activation.
UK setting was also affected, either because it's not universally accepted if the 24 hours is used there, or simply because Microsoft might consider English as "originating" from the US, at least from the point of view of Windows, so English ( UK ) was considered a variant, like Swiss-Italian, Swiss-German, Swiss-French, etc. so it was affected by the same bug, because UK is also set as using 24 hours time format, but there's the AM/PM added to it.
Since most of our users are in the US ( with Germany possibly the 2nd ), and those two settings weren't affected, and I couldn't replicate the problem, because even if I'm located in Switzerland, I'm using Italian ( Italy ) as my settings, because my keyboard has the Italian layout, it took a couple of days to find it, until an user found what it was, so we fixed it.
