Okay, this one took a while.
@BanzaiMan @kris It looks like1 when preparing build VM’s image, you are cleaning out AppData\* directories. You should not do that for AppData\Roaming\Microsoft\Crypto – this is what is causing this error. It turns out, Win10’s rsaenh.dll, unlike Win7, is expecting to always find a couple of certain files there.
1Since Windows builder is not in https://github.com/travis-ci/travis-cookbooks/, I cannot say for sure – or offer a patch