Webmail Problmes

Hi,

i have a huge problem...
All of a sudden, my ISA blocks any request to a Webmail Page (eg:
gmail.com; webmailer.1und1.de, yahoo Mail...)

But the crazy thing is: I didn't change anything! It works fine for 3
Months... until today.
What should i do?

Let me give you an example:
I try visit http://gmail.com and all what i get is this:

"Network Access Message: The page cannot be displayed

Technical Information (for Support personnel)
Error Code: 502 Proxy Error. The ISA Server denied the specified
Uniform Resource Locator (URL). (12202)
IP Address:
Date: 17.01.2007 14:40:33
Server:
Source: proxy"

What now?
I have an URL Set called "eMail". I added http://gmail.com an allow
"All Outbound Traffic" to this Destination, and it still won't work...

Any ideas?

.