I've deleted the .rot files but still getting the error. I tried loading it (the Shareware version) from Shell and got a little more info this time - a message box popped up headed Smart Filesystem as follows:
SmartFilesystem ADH1: (scsi.device, unit 0)
findextentbnode: findbnode() can't find key 11792103091
error = 0 *returned_bnode=00C7D7A4 (*returned_bnode)->key=906700
Sorry if this relates to something I should know about and be able to fix.