Hi Limnos, thanks very much for your reply.
both external drives came preformatted for Windows but I erased each and reformatted them for Mac before using them.
i made the destination folder on the new WD drive the new iTunes folder using Advanced preferences in iTunes.
my original iTunes folder on the first drive contained all my iTunes files, as that, also, was the destination folder that was linked via Advanced preferences.
If I download new content now with the new drive attached, iTunes has no trouble finding where to place the files.
in Preferences I have both boxes checked (copy files" and "organize") that deal with copying iTunes files.
When I first attempted to copy all iTunes files from one media folder to the other on the external drives, I just did a drag and drop of the whole iTunes media folder from one to the other while both were mounted on my desktop. It started copying immediately with no problems, but as it progressed it started skipping files, each time displaying the error message I reported earlier. that included my entire Music folder. When I open, for example, a season folder that contains files that would not copy, eg, Modern Family Season 5, the episodes that won't copy are there and visible but any attempt to drag and drop them into the correct folder on the new drive results in the error message. There is no pattern to it; it will choose some episodes from some seasons but not others, and no music at all.
when I look at the "missing" files in iTunes they have the small exclamation mark that indicates the file is missing, but when I locate it through iTunes it doesn't copy the file on the old external drive to the new one. It just plays it having found the file on the old drive.
originally I had to make the iTunes folder on the old drive into a shared folder using the Get info window after either a software upgrade or an OS upgrade (I can't remember which, it was several years ago). For some reason the upgrade changed the preferences of that folder to a Read Only folder and after researching the problem found the only way to keep using the drive was to make the folder a shared one. I can't remember why and I apologise for that but it was a long time ago.; I can tell you that at the time it was necessary.
thanks again for your time; I have a good working knowledge of iTunes and Macs in general so I truly believe I have done everything according to how it should be done,, but clearly I've done something wrong!
