Bill will be able to help with XaReg error messages, but remember that XaReg has no installer or Uninstaller. It is a stand-alone program.
The error is a .net one, so perhaps a recent Windows update has gone fubar for for some reason?
A few ways to approach this, eg; reinstall the latest .net framework or jump back to the most recent restore point would be two of them.

Xtreme doesn't use .net as far as I am aware, so the problems you have there seem unrelated.