Good sir,
A thousand thanks (plus VAT); that did the trick. After a certain amount of faffing around, examination of chicken's innards and things like that...
I use Onyx to clear all caches every week, but Mr Google suggests it may ignore some, depending on how it feels. Or something. I hope that may be useful for any other Mac user who's having trouble with Jet Blast.
Whence I shall now repair.
Again, thank you.
Happy days,
Ol.