maybe then it's wrong the unit number (scsi id) of the default setup of the part program. try this: click on the icon of the program and with right mouse button pressed search in the menu of the workbench a command like this:''info'' or ''disk info''(i don't remember anymore...) and click on that. it will appear a window with some informations of the prep program. somewhere there maybe there is writen something like ''scsi.device'' or similar and a ''unit x'' or ''scsi id x''.
change this numbers of the id between 0-7, and it is possible that one of this will work.