A little while back I ran into an issue where I was trying to get a new certificate to work on a Windows XP (full patched) box, but for the life of me it just would not work. I spent a lot of time going through and checking the usual suspects (typo with the name, valid dates, certificate chain, etc.) and I finally came across these two interesting links regarding Windows XP and SHA2:
It would seem that you can get it to work in most cases, however some things just aren’t going to be supported. The first link actually has a real nice table detailing what will and will not work.
Long story short, XP is dead and it will only get worse as time goes on.