OK....after a bit more thorough searching through the forums I discovered this post.........
I've seen this error before if the Asterisk was disabled:
go to the web admin page (type your core's IP in a browser) and from the upper menu, choose wizard / devices / core and see if the 'Asterisk' check-box is checked.
Once I've checked it again, at the next reload, the error dissappeared.
But it might be another reason for it, too.
Which seemed to fix the problem. Now lets see what problems crop up next...........................