XML Schema Compilation Error for Valid XML Schema?

I am working with the following XML schema:

<?xml version="1.0" encoding="utf-8"?><xs:schema
	targetNamespace="http://tempuri.org/XMLSchema.xsd"
    elementFormDefault="qualified"
    xmlns="http://tempuri.org/XMLSchema.xsd"
    xmlns:mstns="http://tempuri.org/XMLSchema.xsd"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:uk-gcd="http://www.companieshouse.gov.uk/ef/xbrl/uk/fr/gaap/ae/2009-06-21"><xs:import
	schemaLocation="http://resources.companieshouse.gov.uk/ef/xbrl/uk/fr/gaap/ae/2009-06-21/uk-gaap-ae-2009-06-21.xsd"
	namespace="http://www.companieshouse.gov.uk/ef/xbrl/uk/fr/gaap/ae/2009-06-21"
	/><xs:element
		id="uk-gaap-ae_NameAccountants"
		type="uk-gcd:nonEmptyStringItemType"
		name="NameAccountants"
		nillable="true"
	/></xs:schema>

When I load this schema in Visual Studio 2013's XML Schema Explorer, I can see the uk-gaap-ae_NameAccountants element and its type, which is the nonEmptyStringItemType found in the uk-gcd namespace. All is well.

However, I run into problems when I try to compile the schema within code:

var schemaReader = System.Xml.XmlTextReader.Create("my.xsd");
var thisSchema = System.Xml.Schema.XmlSchema.Read(schemaReader, null);
var thisSchemaSet = new System.Xml.Schema.XmlSchemaSet();
thisSchemaSet.Add(thisSchema);
thisSchemaSet.Compile();

The compilation call throws an XmlSchemaException:

System.Xml.Schema.XmlSchemaException was unhandled by user code
  HResult=-2146231999
  Message=Type 'http://www.companieshouse.gov.uk/ef/xbrl/uk/fr/gaap/ae/2009-06-21:nonEmptyStringItemType' is not declared.
  Source=System.Xml
  LineNumber=14
  LinePosition=3
  SourceUri=file:///C:/Users/jferguso/Desktop/WorkItem10871.xsd
  StackTrace:
       at System.Xml.Schema.XmlSchemaSet.InternalValidationCallback(Object sender, ValidationEventArgs e)
       at System.Xml.Schema.BaseProcessor.SendValidationEvent(XmlSchemaException e, XmlSeverityType severity)
       at System.Xml.Schema.Compiler.CompileElement(XmlSchemaElement xe)
       at System.Xml.Schema.Compiler.Compile()
       at System.Xml.Schema.Compiler.Execute(XmlSchemaSet schemaSet, SchemaInfo schemaCompiledInfo)
       at System.Xml.Schema.XmlSchemaSet.Compile()
       at JeffFerguson.Test.Gepsio.WorkItemsTests.WorkItem10871Test() in c:\Users\JFergu99\Source\Workspaces\gepsio\JeffFerguson.Test.Gepsio\WorkItemsTests.cs:line 108
  InnerException:

Why does the type appear correctly in Visual Studio but cannot be found during compilation?