Thanks for the replies Pete and Giuseppe.
The PCs run 24/7 and the scheduled 4:00 am scan runs on time.
The 4:00 am scan is the only one showing in the GUI. I'm not sure what you mean by a location awareness policy Pete.
They didn't have an earlier version installed. I had a look at the registry but none of the keys mentioned in the document exist on the clients.
I was going to try the tool anyway but I couldn't see a way to get it from Tech Support without paying to open a case.
I think I should just reinstall SEP on one of the clients and see if that fixes it.