Hi, Paul A schrieb am 30.01.2016
It appears that the Koha/Let's encrypt certificate will never work on WinXP
No, it won't. XP was dead before LE was born. It will probably not work for other ancient stuff, like pyramids. Wikipedia[1] says
On April 14, 2009, Windows XP exited mainstream support and entered the Extended Support phase; […] Extended support ended on April 8, 2014, over 12 years since the release of XP; normally Microsoft products have a support life cycle of only 10 years.[118] Beyond the final security updates released on April 8, no more security patches or support information are provided for XP free-of-charge; "critical patches" will still be created, and made available only to customers subscribing to a paid "Custom Support" plan
I don't know how much money you would have to put into the paid "Custom Plan" for something like this to happen, but since the rest of the world does not have a paid "Support Win XP forever" plan, it's not really their problem either. If XP still works for you, cool. If it does not, well, there have been a few new versions now to choose an upgrade from. Or switch to GNU/Linux, I hear it's quite good. -- Mirko [1] https://en.wikipedia.org/wiki/Windows_XP#End_of_support