Problem WebService calling COM+ proxy

I'm trying to make a call into an unmanaged COM+ component via it's application proxy from a .NET ASP Web service. This works fine from a vb.Net Console app, but I get a 'InvalidCastException : QueryInterface failed' exception when the call originates from an IIS hosted application. This leads me to think that the problem is Security related but I would expect to see an 'Access is denied' error if this was the case. The steps i've gone through are :- 1) Application Server Create VB6.0 Single threaded ActiveX DLL 'MyServer' Create a class 'Test' with one method GetString() - that simply returns a string. Create COM+ Application to run as a specific user Create COM+ Application proxy 2) Web Service Server Install COM+ Application Proxy Create ASP.Net Web Service and virutal directory Add COM reference to the COM+ App proxy DLL Using webservice stub add code to create and call COM component :- dim str as string dim svrObj as myServer.Test svrObj = new myServer.Test str = svrObj.GetString() *****Exception thrown here****! Message = 'QueryInterface for interface myServer._Test failed' Any suggestions for a fix gratefully accepted! Thanks