COM+ issue using interop services under Windows 2003

[nhaughton]

I have writtten a webservice in .Net 1.1 using C#, that exposes an existing COM+ application as a webservice to remote web applications.

The COM+ application works fine under Win 2000, XP amd 2003. and the webservice works fine under Win2000 and XP.

However I have been unable to get the webservice working with our COM+ application on a Windows 2003 server, although I can use the same COM+ application from a Windows forms application on the same server. The issue appears to be between the webservice and COM+ interface, but only under Windows 2003.

This is the error I get:

System.Web.Services.Protocols.SoapException: Server was unable to process request. ---> System.InvalidCastException: QueryInterface for interface MTSAdServer.IAdServer failed.
at MTSAdServer.AdServerClass.ReportVersion()
at IHSti.AdvertServer.WebService.IHSti_AdvertServer_W ebService.ReportVersion()
--- End of inner exception stack trace ---
at System.Web.Services.Protocols.SoapHttpClientProtoc ol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall)
at System.Web.Services.Protocols.SoapHttpClientProtoc ol.Invoke(String methodName, Object[] parameters)
at IHSti.AdvertServer.Webservice.Tester.IHStiAdvertSe rver.IHSti_AdvertServer_WebService.ReportVersion()
at IHSti.AdvertServer.Webservice.Tester.WebForm1.btnR eportVer_Click(Object sender, EventArgs e)

Is this a legitimate Windows 2003 security issue, or something about COM+ that is broken beyond repair, or do I have to do something in my webservice that is not necessary under 2000 or XP?

TIA

Neil Haughton