Hi Musket, I've checked for any updates available and none are showing: they usually DO show up in Apps or other alerts if there are any to be downloaded: but I'll check again. Will re-try later with a different file in case it just didn't like that particular track! I have recently updated iTunes. BUT
Well whaddaya know......just as I was typing this, an alert appeared on Apps, and guess what? One for OSX and one for Garageband - tho' the latter is more for drumming loops and hip-hop stuff - not my scene! But if I'm lucky there'll be some bug fixes too!

Leeneia, I use Garageband for uploading my own recordings from H4 Zoom and then edit starts and finishes so that I don't get any unwanted stuff before and after the actual tune: can also cut/copy/paste/rejoin (remove the bad bits!), which I don't think is possible on iTunes.

But thanks to both of you: will let you know once i've installed the updates!