I am having the same problem, just recently.
I also have 2 NEOTVs and they both act the same--don't work now after having worked for years.
I have tested them on my CenturyLink home DSL network and my Verizon MiFi--neither work wired or wirelessly.
I have tested 2 of my iPads, my Android phone, 2 laptops, and 1 desktop--they ALL WORK!
The problem has to be with something that changed on the Slingbox app on NEOTV or in the Slingbox unit itself.
My error is:
Unable to connect to Slingbox. Please check
that your Slingbox is on and connected to the
network. Then try again. (code: 7)
Well my Slingbox IS connected to the network or it wouldn't be working with my iPads, and other computers.
I have reset both NEOTVs to factory, I have rebooted the routers, nothing has solved the problem.
Please help, these 2 NEOTVs are my only source of entertainment for the winter.
I was having a similar problem a few months ago. Sometimes it would drop while I was watching TV and sometimes it just wouldn't connect at all. The other thing I noticed around the same time was that it was taking forever to load the Slingplayer app from the NeoTV homescreen...sometimes I'd wait 4 or 5 minutes just to get that HTTP Error message. After trying several things at home, I finally decided to try it from another location...lo and behold it worked fine. I concluded that it was the quality of my DSL connection and then called my ISP to come and check my line. They gave me a new modem and I haven't had a problem since.