XP isn't a supported OS for .NET 4.5. This is a known issue.
I read a few months back that the reason XP can't install 4.5 is because there are kernel API that 4.5 calls which don't exist on XP. I also read that it would be possible to inject your own implementation of the 'new' kernel calls to an XP machine - and 4.5 could run.
I can no longer find this information. Does anyone know more about this?
A second, but related, question is - how can I take upgraded .Net 4.0 libraries from a windows 7 machine (which had 4.5 installed) and inject them into an xp machine? I believe I read that the implemention files of 4.5 are actually the same as the 4.0 files, there are not two sets. And in fact, the two .net folders (4.0 and 4.5) are only the interfaces - which link back to these same files. If this is the case, then a manual injection of the 4.0 files would likely need the solution to my first question.
In short - does anyone have more information about hacking/manually upgraded .net for xp?