CWA 401.2 Error

When I attempt to access the CWA URL I'm presented with the following
error:
HTTP Error 401.2 - Unauthorized: Access is denied due to server
configuration.
Internet Information Services (IIS)

I have gone through the removal and re-installation of the
Communicator Web Access role multiple times and the issue persists.
The system is a 64-bit Windows 2003 server dedicated to the CWA role;
no other OCS roles are running on this system.  Doing some
troubleshooting I've discovered that if I add the default DOMAIN
\CWAService account to the local Administrators group CWA renders
without an issue and I'm able to log into it without issue.  It is
only when DOMAIN\CWAService is a standard user, which I believe is the
default, is when the issue happens.  This points me in the direction
of a security / permissions issue, but where?

I'm not seeing any events in the event log that would indicate any
type of issue loading the cwaauth.dll ISAPI filter nor am I seeing
anything regarding permission failure.  Running filemon and regmon I
don't see any type of access denied errors.  I'm at a loss as to what
is causing this.  This is a fresh intall of OCS within an Exchange
2007 environment.  Any assistance would be much appreciated.  I don't
really want to run CWA as a local administrator to get this to work.

It should be noted that this is OCS R2.

Thanks.
-matt