Download file from URL not working from Unity Editor Extension Window


I am facing one potential issue while creating editor extension of unity3d.
I am not able to download file from url when i call any function from editor extension window button. Whereas if i create console solution in monodevelop i am able to do so.
Do i need to set any proxy in unity or any other configuration needed? I don’t see any packets sent from unity?
The same issue i am facing with json parsing also.
Please help me.

Thanks & regards,