Upgrade to Windows 2003 breaks WSUS

Hello,

We are slowly upgrading to Windows 2003 server at our sites. We are running
WSUS build 2.0.0.2620 on Windows 2000 sp4 machines and as we upgrade them to
Windows 2003 server sp2 WSUS throws up an error when I connect to the
WebPage for WSUS:

Server Error in '/WSUSAdmin' Application.
----------------------------------------------------------------------------
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Server cannot access application directory 'C:\Program Files\Update
Services\Administration\'. The directory does not exist or is not accessible
because of security settings.
Description: An unhandled exception occurred during the execution of the
current web request. Please review the stack trace for more information
about the error and where it originated in the code.

Exception Details: System.Web.HttpException: Server cannot access
application directory 'C:\Program Files\Update Services\Administration\'.
The directory does not exist or is not accessible because of security
settings.

Source Error:

An unhandled exception was generated during the execution of the current web
request. Information regarding the origin and location of the exception can
be identified using the exception stack trace below.

Stack Trace:

[HttpException (0x80004005): Server cannot access application directory
'C:\Program Files\Update Services\Administration\'. The directory does not
exist or is not accessible because of security settings.]
System.Web.HttpRuntime.EnsureAccessToApplicationDi rectory() +72
System.Web.HttpRuntime.FirstRequestInit(HttpContex t context) +263

[HttpException (0x80004005): ASP.NET Initialization Error]
System.Web.HttpRuntime.FirstRequestInit(HttpContex t context) +983
System.Web.HttpRuntime.ProcessRequestInternal(Http WorkerRequest wr) +128
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Version Information: Microsoft .NET Framework Version:1.1.4322.2379; ASP.NET
Version:1.1.4322.2379

I have looked around for a fix but I cant seem to find anything. Any ideas??

Thank you,

Pete