What does "iTunes err = -3259" mean?

I turned off "Allow simultaneous downloads" and now it is consistently downloading without a problem.

As I search some I find that it happen because of antivirus:

What seemed to work for me was disabling anti-virus software during the load process. I killed my antivirus and then hit refresh on all of the podcasts that failed with err = -3259 and they all finished successfully.

Long term I think we need to get apple to resolve this issue, but in the meantime you can temporarily disable your anti-virus, complete your downloads and then bring the anti-virus back up.

And some where said that it because parental control:

Some of our users are reporting that unchecking Podcasts from the Parental Controls preference pane has resolved the issue. For some of our customers, simply going into: Edit - Preferences - Parental Control and unchecking Podcasts