First off, I don’t have a fix. I wish I did. If you have a fix PLEASE send it (via comment or contact form).
The problem has been annoying me since I setup WiFi sync.
From all the research I’ve done, I haven’t found any fixes. The problem seems to be caused by the use of WiFi syncing. I think it relates to the WiFi device becoming unavailable while doing a wifi sync. A problem that wouldn’t occur on a normal sync, and that would be unique to WiFi.
You should be able to prevent this by disabling the Wifi Sync (in iTunes click on your device, uncheck WiFi syncing).
There was a fix floating around that had you deleting iTunes folders, and restarting. That didn’t work for me.
As soon as I find a fix, will post a link to it here, and will post it on the blog.