For at least a month now, I have not been able to buy music from the iTunes Store. I get a message that "an unknown error has occurred -1202." I have upgraded to iTunes 10.5.3.3 and turned off all firewalls, but I still get this error.
Did you try turning off your antivirus as well? Make sure your router allows for the neccessary ports to be open. Ports can be found here:
Retrieving data ...