Seems ARIN.net has changed its urls. WHOIS urls in the download log generated by DM still work but are redirected to a REST API. I guess it makes sense to update the URL.
E.g.
http://ws.arin.net/whois/?queryinput=141.241.55.124
becomes
http://whois.arin.net/rest/net/NET-141-241-0-0-1
