Unable to open website

We have a problem with some pages such as:
http://dia.alseasc.com/ 
That when I try to navigate I get the following errors:

Denied Connection VHISPA28 12/12/2013 1:40:48 PM
Log type: Web Proxy (Forward)
Status: 12209 Forefront TMG requires authorization to fulfill the request. Access to the Web Proxy filter is denied.
Rule: Allow Web Access for All Users
Source: Internal (10.3.51.13:58923)
Destination: External (10.50.16.28:8080)
Request: GET http://dia.alseasc.com/ 
Filter information: Req ID: 0aa4bf71; Compression: client=No, server=No, compress rate=0% decompress rate=0%
Protocol: http
User: anonymous
Additional information

Failed Connection Attempt VHISPA28 12/12/2013 1:40:48 PM
Log type: Web Proxy (Forward)
Status: 5 Access is denied.
Rule: Allow Web Access for All Users
Source: Internal (10.3.51.13:58923)
Destination: External (10.50.16.28:8080)
Request: GET http://dia.alseasc.com/ 
Filter information: Req ID: 0aa4bfaa; Compression: client=No, server=No, compress rate=0% decompress rate=0%
Protocol: http
User: anonymous
Additional information

Failed Connection Attempt VHISPA28 12/12/2013 1:42:04 PM
Log type: Web Proxy (Forward)
Status: 10060 A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
Rule: Allow Web Access for All Users
Source: Internal (10.3.51.13:58923)
Destination: External (173.193.222.37-static.reverse.serverquality.com 173.193.222.37:80)
Request: GET http://dia.alseasc.com/ 
Filter information: Req ID: 0aa4bfab; Compression: client=No, server=No, compress rate=0% decompress rate=0%
Protocol: http
User: MYDOMAIN\myuser
Additional information

In the client computer i show the following message:

Error Code 10060: Connection timeout
Background: The gateway could not receive a timely response from the website you are trying to access. This might indicate that the network is congested, or that the website is experiencing technical difficulties.
Date: 12/12/2013 4:52:55 PM [GMT]
Server: TMG2010
Source: Firewall

which is not the problem, because when I try it with an internet connection that is not the proxy can access without problems.
Any idea?
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Luis MouraCommented:
I guess the rule for proxy is blocking or not passing the username to validade on ISA.

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