httpwebrequest - C# Invalid URI: The URI is empty -

hello i'm trying collect data website.

on start collecting links on website. after accessing them. problem when accessing multiple pages of website "invalid uri: uri empty" error showing in pages. these of failed urls.

http://syayoyu.com/category/zensinyokudiet http://syayoyu.com/fruitgranola-6759.html http://syayoyu.com/category/diet/fruitgranola 

accessing browser , accessing them 1 one working ok. when try access in loop error occuring. please tell me wrong it.

this accessing code

httpwebrequest request = (httpwebrequest)httpwebrequest.create(url); request.useragent = "a .net web crawler"; webresponse response = request.getresponse(); stream stream = response.getresponsestream(); streamreader reader = new streamreader(stream); string htmltext = reader.readtoend(); 

list<string> list = new list<string>(){ @"http://syayoyu.com/category/zensinyokudiet", @"http://syayoyu.com/fruitgranola-6759.html", @"http://syayoyu.com/category/diet/fruitgranola" }; foreach (var url in list) {     httpwebrequest request = (httpwebrequest)httpwebrequest.create(url);     request.useragent = "a .net web crawler";     webresponse response = request.getresponse();     //stream stream = response.getresponsestream();     //streamreader reader = new streamreader(stream);     //string htmltext = reader.readtoend();     //console.writeline(htmltext);     using (stream stream = response.getresponsestream())     {         using (streamreader reader = new streamreader(stream))         {             string htmltext = reader.readtoend();             console.writeline(htmltext);         }     } } 

in solution, works fine,so there questions don't know?