I'm also having this issue. Resetting / restarting the Tivo didn't help at all.
It is an annoying black message box floating on the screen saying
Sorry, there seems to be a problem. To fix this please call us on 150... etc
Can't get rid of it !
Also can't see 90% of the channels I'm subscribed to..
I've been getting the same 7400 problem as above since yesterday. My Tivo box was activated after a long phone conversation four days ago and at first was working well except for getting very hot. I have been switching it off overnight for that reason. It was when I switched it back on yesterday that the trouble started. I have tried just about everything in the help and settings section. I'm also getting a message that there is an issue M68 with my account. The only change I have made to my account is to reduce the TV subscription to basic since the loss of channels and the bill page is correct. I'm only getting TV channels 1 to 5 at the moment, plus the radio channels.
Sorry but you've been fobbed off, happens a lot at Virgin especially if it was off-shore you spoke to. Ring up again and insist they send a signal hit to clear error 7400. It would help if you gave a bit more context, is this your main box or an additional box? If you have any additional boxes, are they working? When was the last time you used the affected box? Have your recently received a new box? Etc etc.