Problems viewing XML content

Hello everyone. I'm learning XML and have hit some real roadblocks. The trouble has not been my code. It has been something about both of my computers. The reason I know this is because my XML content has parsed properly on just about all other computers. One thing I've noticed so far about the computers that don't parse it properly is that they have Window 7 on them. I'm not necessarily blaming Windows 7. I just want to know what might be wrong with my particular installation. Let me provide some details.

First, here is the code in the main XML file:

<?xml version="1.0" encoding="iso-8859-1" ?>
<!DOCTYPE solutionbrief [
<!ELEMENT solutionbrief (challenge, solution, standout, partner, quote, summary)>
<!ELEMENT challenge (#PCDATA)>
<!ELEMENT solution (#PCDATA)>
<!ELEMENT standout (#PCDATA)>
<!ELEMENT partner (#PCDATA)>
<!ELEMENT quote (#PCDATA)>
<!ELEMENT summary (#PCDATA)>
<!ENTITY isub "We are a wholly owned subsidiary of Parent Company North America.">
<!ENTITY chal1 SYSTEM "challmf2.xml">
]>
<solutionbrief>
<challenge>Describe the customer's challenges. &chal1;</challenge>
<solution>Discuss our solution.</solution>
<standout>Explain why we're the best.</standout>
<partner>Call attention to our partners.</partner>
<quote>Quote a successful client.</quote>
<summary>Summarize the first page. &isub;</summary>
</solutionbrief>

The issue is that none of my web browsers parse the statement in chall2.xml. Here is the code in the file labeled chall2.xml:

<?xml version="1.0" encoding="iso-8859-1" ?>
<challenge>Like everyone else, you want to be as efficient, competitive and innovative as possible in this challenging economy. To achieve these objectives, however, you must keep your costs low.</challenge>

My browsers parse the XML as shown here:

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE solutionbrief>
-<solutionbrief> <challenge>Describe the customer's challenges. </challenge>
<solution>Discuss our solution.</solution>
<standout>Explain why we're the best.</standout>
<partner>Call attention to our partners.</partner>
<quote>Quote a successful client.</quote>
<summary>Summarize the first page. We are a wholly owned subsidiary of Parent Company North America.</summary>
</solutionbrief>


I get the same result whether I choose to display the xml file in IE9, FireFox, Safari or Google Chrome. My wife also had issues displaying my XML content properly and she is running Windows 7 on her computer; however, my daughter and two of my colleagues can display it fine. My daughter is running Windows Vista and so are some of my colleagues at work. On the other hand, some of my coworkers successfully viewed the XML content properly on Windows 7.

At home, I have a Dell laptop running Windows 7 Ultimate. At work, I have an HP laptop running Windows 7, Enterprise Edition. Both are 64-bit machines with 64-bit versions of Windows 7 (Ultimate and Enterprise, respectively). Both are up to date with all of the latest Windows updates as of today (7/1/2011). I've done everything I know how to do. When I try to view the XML content on a browser, the external entity does not show up. Internal entities are fine. I've tried looking up this problem on the Internet, but the hits are too numerous to sort and none of them seem to address this problem. I hope this is enough specific information to help us arrive at the answer. Thank you.

Bill Graham

I have now verified that I can run the XML properly on a virtual PC loaded with Windows XP. I've been told that is because the security in Windows XP wasn't as robust as the security in 64-bit Windows 7. I can believe that, but what do I have to do now to get around the security features in Windows 7? What implications does this have for markup languages such as XML and JavaScript? Anyone?