I'm having the same problem, depending on who the provider is then you will get one of two messages, either that the firmware is out of date or that the STB is unsupported.
I swapped out my 324 for a new 420 with image 2.20.02-r6-420 but nobody can get it to work, I swapped back to the 324 with image 2.20.02-r4-324 and that works fine. It looks like the servers don't recognise the 420 forb some reason, I'm not sure where the fix lies, with the firmware or the server settings?