I have had itunes since first iphone, and have been able to figure out most issues through trial and error and googling.
I am having the same issue, basically itunes downloads works IF simultaneous downloads IS NOT CHECKED.
This goes for app or podcast downloads. I can watch the screen to see that more than 1 download at a time fails.
Scenario: uncheck simultaneous downloads. Watch as each item (app or podcast) downloads fine, one at a time. Check off the box and see '2 more" programs become active download (3 in total). The one downloading is fine, the other two hang and eventually give error. This repeats until i uncheck simultaneous downloads.
Then one at a time works, I can even righ click the error downloads and retry and works perfect.
Same PC since over a year ago, same OS, I allow windows updates and itunes updates.
I have fiber cable from pole to 6 inches from my router, plenty of bandwidth.
PC quad core, 16GB ram, gaming rig, no resource issues.
SSD primary drive, etc. This is an itunes program or server issue in my opinion.