Glad to hear you're back in business!
I had this as well - for me it was a permissions problem on my Downloads directory.
- Locate your iTunes Media folder by checking Preferences... -> Advanced. It should be listed in the box at the top of the preference panel.
- Check the permissions on that directory to ensure that you have read/write access on it.
- Inside that same directory should be another one called Downloads. Make sure you have read/write to that as well.
In my case, my wife and I share an iTunes library. One of us purchased something and it set the permissions on the Downloads directory to be accessible only by that person. When the other went to purchase something else while logged in to the Mac under a different account, the download attempt gave the same error you saw (8201). Sharing a library can lead to this, but however the permissions get corrupted or reset those are the two places I've found that matter for downloading iTunes content.
Hope this helps someone!