Has anyone encountered this iTunes error before?
Only when buying/downloading content.
We Could Not Complete Your iTunes Store Request.
An Unknown Error Occured (12002).
I just encountered this error when attempting to subscribe to the University of Washington
Annual Faculty Lectures - Video feed on iTunes U. ITunes U is a podcast associated with an educational institution; it functions the same way as a podcast on iTunes.
I looked up the contact information for the admins in charge of the podcast (on uwtv.org in my case). I contacted the admins at 10am on Saturday and reported the error. At 4am today (!) I received a reply from Paul at UW. Paul had fixed the problem on their server and asked me to retry. It worked.
I suggest contacting the admins in charge of the feed and reporting the problem to them. If you look on the Podcast page in iTunes, you may see a grayed-out "!" next to the failed download. If you click on that "!", you'll get a more detailed error message. That error message may help the admins in charge of the podcast feed fix it.
Good luck.