I managed to solve it.
I did check my installed versions of Visual C++ and I had a comparable set of both x64 and x86 libraries to your setup.
I tried installing them again from the Microsoft website, but still the same error.
I then looked at the properties of the Start_as_program.exe icon.
In the section for compatability, I ticked "run this program in compatibility for :" and selected "Windows 7".
It now works :) The uniserver control panel child windows now function correctly. So, I can check server status, etc.
Not sure why the changing of compatibility mode had that effect ?