I'm writting the following XSD, however I'm having problems with it. For whatever reason, I'm not being allowed to use my simple types that I define in my XSD. I'm getting this error: `Cannot resolve the name 'mySimpleType1' to a(n) 'simpleType definition' component.`

```
<?xml version="1.0" encoding="utf-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
    xmlns="http://myNamespace" 
    targetNamespace="http://myDifferentNamespace" 
    elementFormDefault="qualified" 
    attributeFormDefault="unqualified">

    <xsd:simpleType name="mySimpleType1">
        <xsd:restriction base="xsd:string">
            <xsd:enumeration value="Added"/>
            <xsd:enumeration value="Modified"/>
            <xsd:enumeration value="Deleted"/>
        </xsd:restriction>
    </xsd:simpleType>
    <xsd:simpleType name="mySimpleType2">
        <xsd:restriction base="xsd:string">
            <xsd:enumeration value="foo"/>
            <xsd:enumeration value="bar"/>
        </xsd:restriction>
    </xsd:simpleType>
    <xsd:attributeGroup name="myAttributeGroup">
        <xsd:attribute name="attribute1" type="mySimpleType1" use="optional"/>
        <xsd:attribute name="attribute2" type="mySimpleType2" use="optional"/>
    </xsd:attributeGroup>
</xsd:schema>

```