XToolkitObsoleteFunc with C++ otk in Creo 9.0.0.0 for pfcComponentFeat::GetModelDescr()

I am attempting to get a c++ otk creo adding to work with Creo 9.0.0.0. I have the plugin working in 8.0.0.0 and 8.0.3.0 with the following code:

[ I should note that I have used the 8.0.0.0 otk libs to build against as that was the original target version - my issue may just be that I have to build against 9.0.0.0 protk and otk libraries - I will try that if that is confirmed to be the case]

pfcFeature_ptr childFp = childFeatures->get(i);
pfcComponentFeat_ptr compPtr = pfcComponentFeat::cast(childFp);
pfcModelDescriptor_ptr mdlPartInstDesc = compPtr->GetModelDescr(); <== exception thrown here

and ultimately I need to obtain the child model using the Model Descriptor and the current session

pfcModel_ptr childMdl = currentSession->RetrieveModel(mdlPartInstDesc);

However I get an exception pfcExceptions::XToolkitObsoleteFunc
{
Message : "pfcExceptions::XToolkitObsoleteFunc"
MethodName : "pfcModel::Model::Descr<get>"
ToolkitFunctionName : "ProMdlDataGet"
}

thrown when I call compPtr->GetModelDescr(). I do not see this function listed as obsolete in /PTC/Creo 9.0.0.0/Common Files/otk_cpp_doc/Otk_Cxx_RelNotes.pdf