have had exactly this problem with my Windows 7 pc and IPOD Classic. I tried pretty much everything mentioned on this and the Microsoft support group but still had the same problem. Interestingly I have never had this problem when updating my Ipod Shuffle.
However I have resolved this problem and others may wish try this solution out.
I have MacAfee antivrus protection with real time scanning and it appears real time scanning is causing the problem. So when synching my Ipd Classic I now turn off real time scanning (and disconnect from the internet) and the Ipod will happily synch with no problem. When done simply turn scanning back on.
So if you have real time scanning and this problem you may want to give this idea a try.
Best of luck!
Andy L