Update:
When I first started working on my production site several years ago, I didn't initially choose dnn but was writing a site from the ground up. I chose to use Spring.net framework to help manage my objects, layers, some AOP, etc. Then I reversed course and started implementing my existing logic into DNN 5.x site but kept Spring.net. Well before finishing the site DNN 6.0 came out and I upgraded (in development) to that and kept coding which included the ASMX services I had already developed. Then DNN 6.2.x came out with MVC Web Service support. I looked into switching gears and going that route but decided not to since my services were already up and working.
Long/short the error is happening due to Spring.net and my attempt to get Dependcy Injection into my ASMX services. I don't yet know why the Spring.net WebServiceExporter is wrapping my object with an incompatible proxy with regard to DNN 7.00. In many ways I don't care I guess. I've been toying around with using DNN Services to implement Web Services and may convert my ASMX files to it (who needs SOAP anyway?) This is especially so since DNN has its own authentication and securtiy measures in place whereas I had to write my own for my ASMX services.
If I can get Spring to DI my business logic into the DNN Services I'll create, I'll definetely move in this direction which should position my site to be able to go to DNN 7 in the future...after I convert the DNN Services to WEB-API.
For those interested here is the full exception dump I was getting:
NotSupportedException: Cannot serialize interface System.ComponentModel.ISite.]
System.Xml.Serialization.TypeScope.GetTypeDesc(Type type, MemberInfo source, Boolean directReference, Boolean throw ) +5143354
System.Xml.Serialization.XmlReflectionImporter.ImportMemberMapping(XmlReflectionMember xmlReflectionMember, String ns, XmlReflectionMember[] xmlReflectionMembers, Boolean rpc, Boolean openModel, RecursionLimiter limiter) +100
System.Xml.Serialization.XmlReflectionImporter.ImportMembersMapping(XmlReflectionMember[] xmlReflectionMembers, String ns, Boolean hasWrapperElement, Boolean rpc, Boolean openModel, RecursionLimiter limiter) +452
[InvalidOperationException: There was an error reflecting 'get_SiteResult'.]
System.Xml.Serialization.XmlReflectionImporter.ImportMembersMapping(XmlReflectionMember[] xmlReflectionMembers, String ns, Boolean hasWrapperElement, Boolean rpc, Boolean openModel, RecursionLimiter limiter) +5117302
System.Xml.Serialization.XmlReflectionImporter.ImportMembersMapping(String elementName, String ns, XmlReflectionMember[] members, Boolean hasWrapperElement, Boolean rpc, Boolean openModel, XmlMappingAccess access) +289
System.Web.Services.Protocols.SoapReflector.ImportMembersMapping(XmlReflectionImporter xmlImporter, SoapReflectionImporter soapImporter, Boolean serviceDefaultIsEncoded, Boolean rpc, SoapBindingUse use, SoapParameterStyle paramStyle, String elementName, String elementNamespace, Boolean nsIsDefault, XmlReflectionMember[] members, Boolean validate, Boolean openModel, String key, Boolean writeAccess) +175
System.Web.Services.Protocols.SoapReflector.ReflectMethod(LogicalMethodInfo methodInfo, Boolean client, XmlReflectionImporter xmlImporter, SoapReflectionImporter soapImporter, String defaultNs) +3245
[InvalidOperationException: Method RenterWS.get_Site can not be reflected.]
System.Web.Services.Protocols.SoapReflector.ReflectMethod(LogicalMethodInfo methodInfo, Boolean client, XmlReflectionImporter xmlImporter, SoapReflectionImporter soapImporter, String defaultNs) +1784908
System.Web.Services.Description.SoapProtocolReflector.ReflectMethod() +188
System.Web.Services.Description.ProtocolReflector.ReflectBinding(ReflectedBinding reflectedBinding) +1613
System.Web.Services.Description.ProtocolReflector.Reflect() +737
System.Web.Services.Description.ServiceDescriptionReflector.ReflectInternal(ProtocolReflector[] reflectors) +621
System.Web.Services.Description.ServiceDescriptionReflector.Reflect(Type type, String url) +148
System.Web.Services.Protocols.DocumentationServerType..ctor(Type type, String uri) +196
System.Web.Services.Protocols.DocumentationServerProtocol.Initialize() +322
System.Web.Services.Protocols.ServerProtocolFactory.Create(Type type, HttpContext context, HttpRequest request, HttpResponse response, Boolean& abortProcessing) +160
[InvalidOperationException: Unable to handle request.]
System.Web.Services.Protocols.ServerProtocolFactory.Create(Type type, HttpContext context, HttpRequest request, HttpResponse response, Boolean& abortProcessing) +818060
System.Web.Services.Protocols.WebServiceHandlerFactory.CoreGetHandler(Type type, HttpContext context, HttpRequest request, HttpResponse response) +302
[InvalidOperationException: Failed to handle request.]
System.Web.Services.Protocols.WebServiceHandlerFactory.CoreGetHandler(Type type, HttpContext context, HttpRequest request, HttpResponse response) +744088
[TargetInvocationException: Exception has been thrown by the target of an invocation.]
System.RuntimeMethodHandle._InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeType typeOwner) +0
System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks) +640
System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) +38
Spring.Web.Services.WebServiceHandlerFactory.System.Web.IHttpHandlerFactory.GetHandler(HttpContext context, String requestType, String url, String path) +632
System.Web.Script.Services.ScriptHandlerFactory.GetHandler(HttpContext context, String requestType, String url, String pathTranslated) +89
Spring.Web.Script.Services.ScriptHandlerFactory.GetHandler(HttpContext context, String requestType, String url, String pathTranslated) +730
System.Web.MaterializeHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +490
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +375