After adding the missing </eSummaryResult> (which prevented parsing even before validation), it validated without problem for me.

I don't understand why it would fail for you. LibXML is very noisy on error, including download errors. Maybe your version has a bug in it? Or maybe it's picking up the DTD from the system catalog instead of downloading it? (The catalog is basically a schema cache so that you don't need to download the same schemas repeatedly. XML::LibXML doesn't add to the catalog, but it can read from it.)