So I was excited today to download a new audio book and get it onto my iphone. I bought the audio book then went to get it all synced up and bamm I’m hit with an error in ITUNES that says invalid response. So I start messing around and doing some searches and found the answer! I have 64 bit vista, but it seems this also happens on xp as well.
I need to delete the Lockdown folder.
You can find it here on xp C:\Documents and Settings\Owner\Application Data\Apple Computer\Lockdown
and here on vista C:\Users\%username%\AppData\Local Look around it might be in one of the other folders there as well.
I did this then restarted for good measuer and Voila my iphone was syncing with Itunes again!
Hope this helps someone out there.