Q: Bootcamp

I downloaded the same file again...

$ ls -lg Win10_1511_1_English_x64.iso

-rw-r--r--@ 1 staff  4414115840 Feb 21 13:51 Win10_1511_1_English_x64.iso

$ openssl md5 Win10_1511_1_English_x64.iso

MD5(Win10_1511_1_English_x64.iso)= a4fde74732557d75ffc5354d0271832e

Your file's MD5sum matches what I get. You can use this file and burn it to a physical DVD at the slowest possible burn rate and enable verification. Once you have the DVD burnt, please re-run BCA and test.

BCA = Bootcamp Assistant.

Did you burn the ISO to a blank DVD and try to install Windows? Your ISO seems to be correct, since we have matched MD5Sum values.

Your 2011 Mac does not fully support booting Windows from a USB. Users who have used the USB method, have had hardware not working properly. You can try the USB method which requires modifying Bootcamp Info.plist.

Please see

Bootcamp without Optical disc drive

http://forums.macrumors.com/threads/install-a-windows-7-partition-on-mac-osx-wit hout-optical-drive-or-usb.1836959/#post-…

I had exactly your issue.  I had downloaded that file from the Microsoft provided link, having chosen the options for "Windows 10" and "English" before clicking on the 64 bit button to download.  What worked for me was to go back to that link and select "Windows 10 Single Language Version" and "English."  My understanding is that the version you downloaded has multiple versions for install, and that confuses Bootcamp.  (For whatever reason the Single Language Version is nearly twice as big, so my understanding may be wrong.) 

Anyway, that fixed it for me.  (and the current link for that download screen is https://www.microsoft.com/en-us/software-download/windows10ISO in case you're looking for it)