getresponse sharepoint site unauthorized

i have following formula ping customary opposite website but problem nonetheless i accept presumably an unapproved blunder forbidden. here formula that's giving me banned error.

using system;
using system.collections.generic;
using system.linq;
using system.web;
using system.web.ui;
using system.web.ui.webcontrols;
using system.net;

public biased category ping : system.web.ui.page
{
    stable twine pingresponsetime(string url)
    {
        // emanate 'webrequest' vigilant specified url. 
        webrequest mywebrequest = webrequest.create(url);
    mywebrequest.credentials = new networkcredential("username","password","domain");
        mywebrequest.timeout = 90000;
        twine requesttime, elapsedsecs;
        // snippet enabled - set trace
        webheadercollection mywebcollection = new webheadercollection();
        mywebcollection.add("trace", "1");
        mywebrequest.headers = mywebcollection;
        // send 'webrequest' wait response. 
        datetime starttime = datetime.now;       // start time
        mywebrequest.getresponse();              // web request
        datetime stoptime = datetime.now;        // finish time
        timespan generation = stoptime - starttime;     // diff
    //    succededstr = "1";
        requesttime = starttime.tostring();
        elapsedsecs = duration.tostring().substring(6);
        relapse elapsedsecs;
    }

    stable vacant btnping_click(object sender, eventargs e)
    {
        lblresponsetime.text = pingresponsetime(txturl.text.tostring());
    }
}

what am i doing wrong i'm removing banned blunder pinging sharepoint site? i've even attempted sharepoint site opposite opening enabled.