problem with autodiscover.xml

After I discovered OOF was not working I got into searhcing about the autodiscover settings
I purchased and installed a SAN certificate. But OOF still not working.
test-outlookwebservices fails as well and so does the autodiscover test on the outlook client
These tests mange to find the correct URL but then report http status code 500
I also notice that the Application log gets loads of event id 1309 source ASP.NET 2.0.50727.0iIhave attached a sample)
I also try to browse the autodiscover site from IE and get a page with the following error: Server Error in '/Autodiscover' Application, etc,etc
Turned off requirement for SSL and still get  the same error so I assume it is not related to SSL
What can be wrong?
Is it something to do with dot net framework?
I need help.
Thanks

Event Type:	Warning
Event Source:	ASP.NET 2.0.50727.0
Event Category:	Web Event 
Event ID:	1309
Date:		9/15/2008
Time:		11:54:44 PM
User:		N/A
Computer:	MAILSERVER
Description:
Event code: 3005 
Event message: An unhandled exception has occurred. 
Event time: 9/15/2008 11:54:44 PM 
Event time (UTC): 9/15/2008 9:54:44 PM 
Event ID: a55c6a3a7af34b769138c67e8a336505 
Event sequence: 5269 
Event occurrence: 5268 
Event detail code: 0 
 
Application information: 
    Application domain: /LM/W3SVC/1/ROOT/Autodiscover-1-128657911333079644 
    Trust level: Full 
    Application Virtual Path: /Autodiscover 
    Application Path: C:\Program Files\Microsoft\Exchange Server\ClientAccess\Autodiscover\ 
    Machine name: MAILSERVER 
 
Process information: 
    Process ID: 5116 
    Process name: w3wp.exe 
    Account name: NT AUTHORITY\SYSTEM 
 
Exception information: 
    Exception type: FileNotFoundException 
    Exception message: Could not load file or assembly 'Microsoft.Exchange.Diagnostics, Version=8.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified. 
 
Request information: 
    Request URL: https://mail.bdomalta.com.mt:443/autodiscover/autodiscover.xml 
    Request path: /autodiscover/autodiscover.xml 
    User host address: 192.168.2.252 
    User:  
    Is authenticated: False 
    Authentication Type:  
    Thread account name: NT AUTHORITY\SYSTEM 
 
Thread information: 
    Thread ID: 5 
    Thread account name: NT AUTHORITY\SYSTEM 
    Is impersonating: False 
    Stack trace:    at Microsoft.Exchange.Autodiscover.Global.Application_BeginRequest(Object sender, EventArgs e)
   at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
 
 
Custom event details: 
 
For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

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