I went through the same 'ordeal' but recently discovered that the 'problem' was actually the USB power supply. I noticed that the Hub port lights flickered and I too tried a new USB cable--only to discover, later, that it wasn't the cable. The flickering meant that the HUB power was actually acting as an OFF switch, long enough to disconnect and result in the Popup. The part that threw me off was that when I looked at the HUB the lights were back on. It wasn't until I noticed the flickering AND then the popup that I realized the two events coincided and it was a faulty hub power supply.
I replaced the hub with a new hub and it's power supply and it cured the problem. Why didn't I just replace the old hub's power supply you ask? Because the hub was 9 years old and replacing the power supply was not an option--and for $30.00 I got a new 7 port Belkin w/ a new power supply for less than what the original one cost.