The issue with the file you attached is that we do not yet support opening files from a https:// URL. This also effects the schema tagging for color coding. You can stop the error messages by turning off (Document > XML Options... > Color Coding > Language > "Use schema for color coding")
I am going to look into this, but it may not be practical to implement quickly.
I have found that I can fix our Xerces based XML validation to handle this though, so that fix will be in beta3.