Validation problem when SCHEMA XSD and ENTITY DECLARATION

I have a xml file which looks like to the following one. It is linked to a schema file, and has, at the beginning, a DOCTYPE tag which refers to jpeg ENTITY. 
I note that the schema takes in account the Entity but I can't valid my xml file with MSXML2 because of mix Schema and Entity. I only use the load function of msxml2 that valids a xml file according to its schema. but it doesen't work when Entitys are in declaration.
Have you got an idea?

Yours faithfully 

<?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE xml [ <!ENTITY Image_3 SYSTEM "Image_3.jpg" NDATA JPG> ]> 
<xml xmlns:xsi="<http://www.w3.org/2001/XMLSchema-instance>" xsi:noNamespaceSchemaLocation="Schema.xsd"> 
<tag1>
 <tag2>
 <tag3>
 <tag4> . . . 
<tag5 type='Image_3'/>
 </xml>