What happens is that the tiff structure is damaged in the RAW file. This can happen due to a fragmented harddrive or can happen on an external harddrive that is not storing the imagedata correctly. This can also happen on a CF-card that contains bad segments. This is why we always recommend to only use known brands and that the CF-card is always reformatted before starting a job.
However we suggest to try and rescue the files although we cannot promise that all files can be rescued again. This goes for image data on internal/external harddrives as well as CF-card's.
Please install the program "Hex Edit" following the link below.
Open the damged file in the program Hex Edit. Then you select the first 8 bytes, until the signs "IIII" or "MMMM" appear. Then delete these 8 bites. After that make a "save as...." and save the file under the same capturename BUT with the extension .cap and NOT .tif. After this most files can be seen again.
Please note that Phase One cannot gurantee that all files can be rescued again due to errors from harddrives or CF-card's.