TMG errors

Dear all,

I am using TMG 2010 with the Websense Filter (7.5.0) and I have recently had problems with accessing a particular website.

Also I have ran some logging on the TMG server and I got the following: 

Allowed Connection SERVERNAME 2/13/2014 10:54:52 AM 
Log type: Web Proxy (Forward) 
Status: 301 Moved Permanently 
Rule: RULE NAME 
Source: Internal (x.x.x.x:57554) 
Destination: External (50.63.202.25:80) 
Request: GET http://www.thefdforum.co.uk/ 
Filter information: Req ID: 179991df; Compression: client=No, server=Yes, compress rate=0% decompress rate=0% 
Protocol: http 
User: domain\username 

The proceeding logs show the following status:

407 Proxy Authentication Required

12210 An Internet Server API (ISAPI) filter has finished handling the request. Contact your system administrator. 

The web page displays HTTP 443 Forbidden