Just ran MVT and it did find a Registry error in VS which it fixed. Will see if that solves the problem on the next daily update.
UPDATE: On the next update , everything went as it should. Registry issue seems to have been the cause.
I don't know if this is connected, but I keep getting a message saying that mcupdate.exe has had to close because of an error and I need to restart it. Restarting seems to be automatic when an update is requested.
There are McAfee logs aplenty in C:\Documents and Settings\All Users\Application Data\McAfee\MCLOGS but you'll have to look for one called mcupdate and there are several with that name. Possibly the right one for this is in ..\MISP\mcupdate, but I couldn't swear to it. A disturbingly high number of these log files contain error messages, but I haven't a clue what they mean. So long as MVT isn't kicking up a fuss I do my best to forget that those log files are there.