Why do I receive an error page telling me that an UnauthorizedAccessException happened when I use Microsoft Internet Explorer (IE) to test Outlook Mobile Access (OMA) connectivity?

OMA requires the Windows .NET Framework and ASP.NET. If you install these components on your server and promote the server to a domain controller (DC), the Dcpromo process changes the ACLs for the ASP.NET code, which results in the error that you reported. The Microsoft article "XCCC: "Server Error in '/OMA' Application" Error Message When You View the Outlook Mobile Access Web Site" (http://support.microsoft.com/?kbid=818486) describes how to fix the problem by using the ASP.NET registration tool to reset the ACLs.