SnoopZ's post inspired me to look on the VM forum to see what happened last time. I found the original thread relating to the lack of updates for trial boxes and discovered that last time I did a full factory reset and restore in order to make it pull the update.
So I did a backup, did the reset, then logged back in with the default password (although it also wanted the WPS PIN - I had to crawl behind loads of junk to find that on the bottom of the box).
Then seeing as it was now on V2.01.03 I went into the restore dialog to be faced with:
There didn't seem to be a way to point to the name of the backed up config file, the text box wasn't accepting input and the selection button was absent.
I did another power cycle and tried again with the same result. Eventually I hit refresh in the browser and lo and behold I could choose a file, and all was well. Very odd. It appears to be fine now, but seeing that message gave me an attack of the cold pricklies.