Hello, I have the exact same issue. I've installed Python 3.5 AMD64 from python.org (https://www.python.org/ftp/python/3.5.0/python-3.5.0a1-amd64.exe to be exact), and I've checked the installer MD5sum to be valid. I've selected the advanced install to change installation directory and to precompile standard libs. Upon finishing the installation I was displayed the message twice, the first time about python.exe, and the second about python35.dll, after which the installer finished without reporting other errors.
When launching Python 3 from the console via `py -3` I get the exact same dialogue box (twice: once for the exe and once for the dll), while `py -2` and `py -3.5-32` work with no issue (installed via seemingly the same method, but with the 32 bit installer instead). I wanted to install an x64 version of python because I need additional memory to calculate on large numpy arrays. Regards, -- Mateusz Naściszewski -- https://mail.python.org/mailman/listinfo/python-list
