Unable to perform schema validation with xmllint

[TShapinsky]

when running xmllint --noout --schema BuildingSync.xsd <BuildingSync xml> I get this error

Failed to locate a schema at location 'http://www.gbxml.org/schema/6-01/GreenBuildingXML_Ver6.01.xsd'. Skipping the import.
BuildinSync.xsd:1820: element element: Schemas parser error : Element '{http://www.w3.org/2001/XMLSchema}element', attribute 'ref': The QName value '{http://www.gbxml.org/schema}Area' does not resolve to a(n) element declaration.
BuildinSync.xsd:1821: element element: Schemas parser error : Element '{http://www.w3.org/2001/XMLSchema}element', attribute 'ref': The QName value '{http://www.gbxml.org/schema}Volume' does not resolve to a(n) element declaration.
BuildinSync.xsd:1822: element element: Schemas parser error : Element '{http://www.w3.org/2001/XMLSchema}element', attribute 'ref': The QName value '{http://www.gbxml.org/schema}PlanarGeometry' does not resolve to a(n) element declaration.
BuildinSync.xsd:1827: element element: Schemas parser error : Element '{http://www.w3.org/2001/XMLSchema}element', attribute 'ref': The QName value '{http://www.gbxml.org/schema}ShellGeometry' does not resolve to a(n) element declaration.
BuildinSync.xsd:1832: element element: Schemas parser error : Element '{http://www.w3.org/2001/XMLSchema}element', attribute 'ref': The QName value '{http://www.gbxml.org/schema}SpaceBoundary' does not resolve to a(n) element declaration.
WXS schema BuildinSync.xsd failed to compile