I have 2 VOOM boxes, one is connected to my HD set, the other to a SD set.
The SD set box has only locked up once in about 5 weeks---and it did so "on it's own". Turned on the TV (the box was on already) and it was locked up--stuck on one channel with no key response.
The HD set box freezes much more frequently usually every 2-3 days. Sometimes it just freezes up "on it's own" as above, other times it just goes berserk with channel numbers not matching up to the actual onscreen channel.
I wish I knew what the difference was, and whether or not the HD set box is defective, or at least, more so than the other box. I haven't tried switching them, since it's such a pain to get behind my component setup--