Using excel object on IIS 7 causes COM class failure

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ASP.NET

C#3.5

MS-Excel

I'm using the following in an ASP.Net function:

Microsoft.Office.Interop.Excel.Application app = new Application();
double result = app.WorksheetFunction.ChiInv(probability, degreeOfFreedom);
app.Quit();
return result;

The above works fine on my development box. When I publish to the web server and try to run the code I get the following:

Retrieving the COM class factory for component with CLSID {00024500-0000-0000-C000-000000000046} failed due to the following error: 80070005.

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.UnauthorizedAccessException: Retrieving the COM class factory for component with CLSID {00024500-0000-0000-C000-000000000046} failed due to the following error: 80070005.

ASP.NET is not authorized to access the requested resource. Consider granting access rights to the resource to the ASP.NET request identity. ASP.NET has a base process identity (typically {MACHINE}\ASPNET on IIS 5 or Network Service on IIS 6) that is used if the application is not impersonating. If the application is impersonating via <identity impersonate="true">, the identity will be the anonymous user (typically IUSR_MACHINENAME) or the authenticated request user.

To grant ASP.NET access to a file, right-click the file in Explorer, choose "Properties" and select the Security tab. Click "Add" to add the appropriate user or group. Highlight the ASP.NET account, and check the boxes for the desired access.

I've tried following the instructions to no success.

Any ideas how I can get an ASP web page to have access to an excel function?

Thanks!
Don