Small Business Server, Proxy Server 2.0 Internet Access Problem

My LAN is running behind proxy server 2.0 and Microsoft Small Business Server. The problem is, every once in a while, I am unable to surf web pages, and every time I input a site address, I am sent to my intranet default web page. If I disable the connection through the proxy server on my browser, I can surf the web as normal. However, I am trying to prevent web surfing without using the proxy server. Any ideas as to what I can do, while still surfing the net and using the proxy server??

Thanks for ANY help