Hi Brent,
Thanks for reply, I am trying to create SOE propoerty page so I have added ESRI.ArcGIS.SOESupport.dll as a reference in my solution but still don't find this interface "IServerObjectExtensionConfigurator".
I following this example at the second part to create the property page for SOE :
ArcObjects 10 .NET SDK Help
Thanks,
Ammar Assem.