[CONNECT C++] How is Bentley::DgnPlatform::XDataTreeNode::GetECInstanceBySchemaName() parameter specified

I've got an ElementTemplateNodePtr and I want to call GetECInstanceBySchemaName() to grab an associated Item from the template. I can never get it to return anything other than nullptr. I have tried using the name of the ItemTypeLibrary ( "SRSFeatureTest" ) and the "fullname" of the library ( "DgnCustomItemTypes_SRSFeatureTest" ), and I have tried to include the name of the Item ( "Backfill__x0020__Area" ) in syntax like "DgnCustomItemTypes_SRSFeatureTest:Backfill__x0020__Area".

I *am* successful when calling GetECInstanceByClassName(L"Backfill__x0020__Area").

Any idea what may be going on with GetECInstanceBySchemaName()?

Thanks

Bruce