Page is not displaying getting an error 502 Proxy server ISA SERVER denied the Access

I have a database program (using SQL) that I am trying to communicate to on the SBS 2003 Server. When I go onto my client PC and open the database program up from the web  it opens fine however some instances I get a 502 error saying the ISA server denied access.

I am running ISA 2004 on my SBS 2003 Server Machine and Windows XP Pro SP3 on my client PC logging in online using the latest Firefox update.

How can I configure the ISA server to allow access? Like I said it doesn;t always trigger the error some times the connection works just fine.
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I don't even have a good starting point to work from.

Start with knowing exactly what the proxy is denying.  The Error page in the Browser Window will tell you that,..just read all the details.   The Monitoring Log in the ISA MMC will give you more details,...don't be afraid to add additional Fields to the Log Display to gain more information.

A lot of authentication problems are really DNS problems.  Make sure your DNS Structure is correct.   Take note that #2 and all below that are not ISA settings,...they are OS settings.

1. First Rule in ISA is to allow the AD/DNS machine to make outbound DNS queries to their Forwarder.  Nothing else should be allowed to make outbound DNS queries.

2. Make sure the External Nic of the ISA has the DNS setting left blank

3. Make sure the Internal Nic of the ISA has only the AD/DNS listed in the DNS specs and that nothing else is listed.

4. Make sure the ISA Nic is listed at the top of the Binding order.
Not my area of expertise but I would suggest checking what open ports are configured - is the port used to communicate with this application changing?

Also, check the ISA logs at the time a failure occurred and see if it logged a block action.
Keith AlabasterEnterprise ArchitectCommented:
No knowledge of Firefox as I only support Microsoft products. Do you get the same issue when using IE?
Confirm you have ISA 2004 SP3 installed.
Open the ISA gui, select monitoring, logging, start query - what messages are you seeing in the realtime viewer when you get the 502? The 502 is generally a permissions issue but if it is intermittent then there could be something else untoward. Is this on an internal PC or an external machine accessing through a published web site?
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It is works ONCE,...then the ISA is correctly configured, is not possible to make a correct configuration "more correct" then "correct".  So, if it is intermittent the problem is likely elsewhere.  It too early in the conversation to speculate more.
cmdolcetAuthor Commented:
What would I need to check to determine the issue? Steps>
Keith AlabasterEnterprise ArchitectCommented:
I think Phil has accidentally left the word 'internal' out of point 4 but as you have not bothered to respond to me I'll move on.
cmdolcetAuthor Commented:
The page cannot be displayed
Explanation: There is a problem with the page you are trying to reach and it cannot be displayed.

Try the following:

    * Refresh page: Search for the page again by clicking the Refresh button. The timeout may have occurred due to Internet congestion.
    * Check spelling: Check that you typed the Web page address correctly. The address may have been mistyped.
    * Access from a link: If there is a link to the page you are looking for, try accessing the page from that link.

Technical Information (for support personnel)

    * Error Code: 403 Forbidden. The server denied the specified Uniform Resource Locator (URL). Contact the server administrator. (12202)
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