This is the standard panic response when Unix cannot access a critical piece of hardware for a process. In this case for some reason unix cannot access the /usr/data directory. When ever it trys, it fails and crases the system. Why it fails, I cannot even begin to tell you, with the limited information you gave.
When you start to see this sort of errors it means most likely that the hard drive is dying.
Some part of the disk has lost informations and sco could NOT recover it.
I would sugest you to relpace that drive.
another possibility is with a drive array with the write back cache enabled is the battery on the controler is dead and the controler lost/corrupted part of the info before comiting it to the drive.