Well, it sounds like it simply isn't a valid XML file.
If you print out the result of sr.ReadToEnd() instead of calling XElement.Load, what does it look like? If you try to load the file into an XML editor, what happens?
Btw, it's better to use a using statement than calling Dispose explicitly: with your current code, the StreamReader isn't disposed if Load throws an exception.
Finally, is there any reason you're not just using XElement.Load(documentationFileLocation)?