If you are getting "404 Aborted on Request" it means your machine is terminating the socket before ScrapeBox could receive a reply. So try dropping your threads, and raising the timeout to suit your connection a bit better.
I get this issue a lot after a little while. Proxy checker works great for a while, then after checking a couple hundred, it goes into 404 mode. It's as if my Windows XP just gives up or my ISP no longer allows anything for a while.
Reducing connections and increasing timeout doesn't seem to work. It still eventually happens.
Is there something in XP I might be able to change here? Or might it be my ISP?