Ryan Neve added the comment:
Turns out I had accidentally installed 3.4.3 32 bit over 3.4.1 64 bit. I
re-installed 3.4.1 32 bit, then un-installed it, then I was able to install
3.4.1 x64.
I also tried installing and un-installing 3.5 which worked fine but didn't fix
any
New submission from Ryan Neve:
Much like issue 22648. Windows 8.1, I had version 3.4.1 and installed 3.4.3
without first uninstalling earlier version. Tried uninstalling older versions
and it failed with:
A program required for this install to complete could not be run.
Windows uninstall
