Wifi sync error -50
Whenever my wife's iPhone 4 attempts to sync over wifi using the new iTunes 10.5 and iOS 5, it aborts with a message that sync could not complete due to unknown error (-50). The phone syncs just fine if I connect it directly to the computer using a cable. My iPad 2 also syncs fine to the same computer using wifi sync so I know wifi syncing is possible on my network. The only help I can find on -50 errors relates to USB drivers and such which obviously doesn't apply to wifi.
Any hints as to what this error means and how to solve it?
iPhone 4, Windows 7