4. Click Update now and wait a few seconds. You should see a message confirming the clock synchronization. If not, try again, or select a different server and then try.
5. Click OK to exit, then head to iTunes and try your purchase/code redemption again. This time, it should work!
So, think this is another case of Apple messing with Windows users? Somehow I don't think this problem exists on Macs. Hmmm.