boot camp 6 update for windows 10 will not finish install

Like the title says.

It says is has downloaded and is installing. The progress indicator gets to a certain point and stops. Forever. There are no error windows, nothing.

I updated Boot Camp via Apple Software Updates in Windows 7. Then upgraded to WIndows 10. Then ran Apple Software Updates again and it just sits there doing nothing. There are various setup.exe's running, somethin from RealTek, but none of them are using any CPU.

What do I do?