Hello.
Certain types of software can affect the way a computer sends and receives information from the Internet. This article may help you resolve the issue:
Information about error -50 and downloading videos
http://support.apple.com/kb/TS1583
If it did not work, contact iTunes Store via (http://www.apple.com/support/itunes/store/ ) and/or Apple Tech Support via 1-800-275-2273.