How to fix error 5010F (26)?

I have downloaded macOS sierra from app store. It was downloaded well but when I tried to installed it on my macbook air at the mid of the process i got a pop up that macOS sierra can't be installed. So, i restarted my device. But, It wasn't boot to the previous macOS x el capitan. When i use to type my password and press enter, device use to restart. I tried couple of times than i preferred to use recovery option and unmount my hard drive and earse it to install OS Mountain Lion. I have tried using Command + R first it asked for wifi connection I did it successfully (note : I have WPA WPA2 security installed as well). But at the end of the Internet Recovery timeout it give me error 5010F (26). I have again tried by pressing OPTION key with power button. It has asked for wifi connection and than internet recovery. Eventually result was same "error 5010F (26)". Could you please help me to fix this? I'll really appreciate it. Thanks!