Q: An unknown error occurred (-50). There was an error in the iTunes store. Please try again later.

Refer to this article:

iTunes Store: "Error (-50)" when downloading purchased content

http://support.apple.com/kb/TS1583

Try reset winsock and see if error will go away.

Close your iTunes,

Go to command Prompt -

(Win 7/Vista) - START/ALL PROGRAMS/ACCESSORIES, right mouse click "Command Prompt", choose "Run as Administrator".

(Win XP SP2 & above) - START/ALL PROGRAMS/ACCESSORIES/Command Prompt

In the "Command Prompt" screen, type in

netsh winsock reset

Hit "ENTER" key

Restart your computer.

If you do get a prompt after restart windows to remap LSP, just click NO.

Now launch your iTunes and see if it is working now.

If you are still having these type of problems after trying the winsock reset, refer to this article to identify which software in your system is inserting LSP:

iTunes 10.5 for Windows: May see performance issues and blank iTunes Store

http://support.apple.com/kb/TS4123?viewlocale=en_US

• Open iTunes.
• On Windows PC: From the Edit menu, choose Preferences.
• Click the Parental Controls tab.
• Place a checkmark next to the option to disable the iTunes Store, and next to the option to Allow access to iTunes U
• Click OK.
• Open iTunes preferences again.
• Choose the Parental Controls tab.
• Remove the checkmark next to the option to disable the iTunes Store.
• Click OK.
• Test the issue.

OK, refer to this thread page 3 who mentioned about deleting the media folder which you had problem with, then re-download your media again. Wonder if you have done that from Article TS1583 above.

https://discussions.apple.com/thread/3590560?start=30&tstart=0