Shortening url using bit.ly

I am creating short urls as we have done with tiny URL, based on the link:

http://www.emadibrahim.com/2009/05/07/shortening-urls-with-bitlys-api-in-net/

But I am getting an error:

The remote server returned an error: (407) Proxy Authentication Required.

Ho开发者_运维技巧w can I resolve this issue?

I'm using C#.

<system.net>  
           <defaultProxy useDefaultCredentials="true"> 
           <proxy usesystemdefault="False" proxyaddress="http://127.0.0.1:8888"   bypassonlocal="True" />  
</defaultProxy>  
</system.net>

by using useDefaultCredentials="true" i can get ride of the problems.