I know you did not want this answer, but please be aware XP is out of maintenance for more than four years now. And even 2014 the concepts of Microsoft networking have been changed since XP was designed.
It might be there is some sort of incompatibility with XP no one has faced so far. We just do not know. And to be honest we do not put any effort in getting an absolutely outdated operating system to work with UCS, sorry.
Even UCS 4.0 has been released after the end-of-life of XP. a (not really serious) hint could be to install UCS 3.x and see if they are compatible.