When I tried to buy a song, I got the message:
iTunes couldn’t download your purchase.
You don’t have write access to your iTunes media folder or a folder within it. Change permissions (in the finder) and then choose Store > Check for Available Downloads.
I suspect that that instruction refers to PCs, not macs (there is no "permissions" in the mac finder).
Problem solved - I contacted "iTunes Support" with my problem and got a response within an hour - the girl/lady sent me a link to a website that tried to help solve such problems - it didn’t, so I then did as she had suggested - 'phoned their "Technical Support". The outcome - a half-hour’s ‘phone call to one lady who then said that she couldn’t help, so she passed me to another lady for another half-hour’s call - the 2nd lady said that she couldn’t help either, and suggested that I ‘phone “Support” again - the very folk who had advised me to 'phone their technical experts. Yuk!
I was surprised to receive a further email from “Support”, some hours later - the girl/lady who I had communicated with first had, with her supervisor, found another website link that aimed to help folk with such problems
Troubleshooting permissions issues in Mac OS X
and, after reading it, I found a suggestion that I hadn't tried - “Applications-Utilities-Disk Utility-Verify Disk Permissions”. I had used that software to check external things previously, and I had even run it to check the HD ages ago - but that had showed nothing wrong, so the idea of using it had not come into my head - it solved the problem. Olé
My conclusions: “iTunes Support” (actually “Rose”) - great; “iTunes Technical Support” - a waste of time & cost of ‘phone call!