Windows 8.1 on Macbook Pro 2011

Hi

I'm trying to install Windows 8.1 on my Macbook Pro 15" 2011 model running El Capitan

I'm using Boot Camp and a 8GB USB

First of all i only have two options starting Boot Camp and not three like i see in a lot of guides about how to do the install.

My options are:

1. Get the newest software for Windows support from Apple

2. Install Windows 7 or newer

After i've marked the two options the download runs, but after it's done i get a message telling me that the installationdisk doesn't exists.

What am i doing wrong?

Thanks in advance