>Not Norton/ZA but there are some processes that run (a few provided by our Corp Network). Could be you are right and it is the cause of the problem as it is intermittent. Thanks for the pointer.

Because this message doesn't ring me any bell, I would say it is coming from the route from this end to your end. It could come from a security in place, a proxy or something similar. If you can, maybe you can disable that tomorrow for the entire day and see how it goes. With the frequency that you know, you will be able to know after a while if that is in effect or not.