I had to do this recently. Its actually easier than I thought it would be. All you need to do is use the standard PS3 folder setup as if you were updating firmware, except you create a folder within the "PS3" titled folder labeled "SAVES" i believe. Its basically the standard location your ps3 would save them to if you go into Save data and try to copy manually using triangle.
Any way copy your saves to this location, plugin your usb to the ps3, then go into ps3 game saves utility. All the saves on your usb should show up on the ps3. Go thru and manually copy each one over.
Other people I have heard suggest you can make them appear doing it the way your doing it, and then using rebuild database, BUT I in NO WAY suggest that, as anytime I have attempted to rebuilid database it ended in a corrupt HD loop that will only let me proceed by formatting my entire HD.
Hope this helps
As far as I know, my ps3 has never had an undetected error.