I've spent the last 2 years in load control and have seen the following errors:
- wrong aircraft registration (so wrong dry operating weight/index)
- wrong pallet weight
- wrong pallet(s) brought out to aircraft
- pallets loaded in wrong position
This is all down to human error and can be detected by simply checking your work (and others) thoroughly. I've seen some crews just take the loadsheet, sign it and hand it back. The dispatcher that used the wrong registration was suspended, I don't know what happened to the captain who signed the loadsheet (the registration is right in front of you on the instrument panel). I guess the dispatcher is there to check that eveything is correct but we all have our part to play. This doesn't include the pressure to deliberately misload by company reps who want to get all there cargo away...
Airbus have a crosscheck on C of G position, the loadsheet figure must be within a certain limit of the indicated figure on the cockpit screen.