I'm really not sure if there's anything else that anyone here can do, since the problem seems to be specific to your setup - Astraweb is proven to work 100% with all Alt.Binz versions. Maybe your ISP is the issue, in which case contact them, or drop Astraweb a query. If you want to eliminate local problems, try installing some network tools - maybe even Wiresahrk to sniff the connection. Try enabling/disabling SSL, use different ports, etc. Check your router logs ... and so on.
This is all assuming of course that you get these errors with *all* NZBs and not just one ...