From our reports it seems that this usually happens on PS3 systems (Sony playstation), but may also happen on others. We also have one report here on the GeekDrop help forums of it happening after they used our Netflix Error AIP-701 hack.
Sometimes it also says:
This device has been deactivated. There could be a problem with your account or it could have been deactivated through Netflix..com
(We have found tweaking the Netflix Help Page's steps to our way usually works a bit better.)
Unplug your devices (any order):
(PS3 or whichever streaming device you're getting the UI-502 error on).
Router / hub or anything similar.
Modem, be it DSL, Cable or whatever.
Let them sit unplugged for about 1 minute or so, to let all the juice out of them, (Pro Tip: pressing any buttons on them may help speed that up a bit.)
Plug them all back in, one at a time, letting them fully go through any power-on routines, in this order:
If for some reason you get the infamous AIP-701 Error, we have the solution here, that has been reported to work very successfully.
If you have any other tips or tricks for resolving the UI-502 error, please post them in our comments! Also, we'd love comments on whether or not this worked or failed for you as well.