VB 2010 + HTMLAgilityPack + Large Processing = Error?

I have spent way too much time trying to sort this little issue out. I have narrowed down the issue to the exact procedure that throws the error. Yes, I have used Google..

Try
Dim tempSource as String = Nothing
Console.WriteLine("Loading document...")

[code]....

I am loading a text file, that contains about 1100 lines, and each line is going to be processed with HTML Agility Pack. From what I can tell, when it runs "doc.loadhtml(richtextbox1)", it throws the error. I also have tried to load the file into a string, and load the string with "doc.loadhtml(thestring)". It doesn't make a difference, still errors.

Here are is a sample of how each line looks:

<Site Index="" Name="" Group="" PR="" />
<Site Index="" Name="" Group="" PR="" />

[code]....

I am using HTML Agility Pack, however the above is what is on every line, about 1100 lines! For testing, I have a smaller text file made of about 50 lines before I load up the 1100 line file ;) There aren't any HTML, HEAD, or BODY tags! They aren't needed for my parsing. I am using HTML Agility Pack because it is easy to parse elements with. I can grab each value easily from each line.

I am not sure if maybe the error is because it technically isn't HTML? Meaning since the loaded code doesn't have an HTML or BODY tag, that it errors? I wanted to get this question posted, and while I am waiting on some answers, I am going to parse the document another way. Just curious as to what the deal is and why HTML Agility Pack isn't working. More of a proof of concept then anything, for my own learning and knowledge.

Here is the error I get (btw the on the doc.load() line, is where it throws the exception):

Object reference not set to an instance of an object

Last Note: The routine is on a background thread. I have used multi-threading before, and have delegates created for deeper in the code.