how to use setpassword Method

Dear frnds ,,
 
Plz help me out ? hoe to use setpassword method for resetting AD password. I m trying bt it is showing some error?
 
string strLogin = txt_usrid.Text.Trim();      
        string strNewPasswd = txt_newpwd.Text.Trim();
        string ADMUSER = "CONFIGADMIN";
        string ADMPWD = "$NEWPASSWORD$";
 
        DirectoryEntry objRootEntry = new DirectoryEntry("LDAP://ITSSBLRDC002", ADMUSER, ADMPWD, AuthenticationTypes.Secure);
            DirectorySearcher objADSearcher = new DirectorySearcher(objRootEntry);
            objADSearcher.Filter = String.Format(@"(& ...