Same problem, I was able to activate it previously but now it's become "unactivated" and produces this same activation error. "Something prevented us from communicating with our activation server. Wait a few minutes and then try again. Error code: 0x87E10BC6"
I found that when I elected to change the product key, and then specified the same product key used to install (the same one provided by Microsoft for Windows_InsiderPreview_Server_vNext_en-us_17733.iso), then clicked 'Activate' in the window following the successful key change, it then activates successfully. Give that a try, if you're still stuck on this.
