A friend of mine had a similar problem and this fixed it (on a Mac):
Click Finder.
At the top menu, click Go.
Select ?Go To Folder? from the submenu.
Type ?/private?.
Open the folder ?etc? and locate the ?hosts? file.
Copy it to your desktop > right click > show info > make sure you have the rights to read and edit it.
Open it in text editor.
Search ?74.208.10.249 gs.apple.com? and ?127.0.0.1 gs.apple.com? (somewhere at the bottom normally)
Add a ?#? and a space before it and save the file.
Copy it back into the ?etc? folder and replace the old ?hosts? file.
Restart iTunes and it should be fixed!
I found this solution on the Apple discussion board, sadly I can't post a URL since I do not have enough posts yet.