Plugin Registration Tool error when debugging HttpWebResponse response

I used the "persist to entity" for the debug  of plugin(due to the fact that my plugin is triggered via Action in javascript so I can only choose this debug option).

Code snippet:

WebRequest request = WebRequest.Create(SVC_URL + string.Format("?methods=3&parameter={0}", _id));

request.Method = "GET";
request.ContentType = @"application/json; charset=utf-8";
HttpWebResponse response = (HttpWebResponse)request.GetResponse();

While I am debugging, it hit an error at:

"HttpWebResponse response (HttpWebResponse)request.GetResponse();"

and I couldn't proceed the plugin debug.

To verify above code is working, I had created a console program with similar code & I am able to "step over" the code during debugging & the code work fine without error.

Any clues why the tool stop working, I am using the 2016 version.

Thanks guys.