This error means the program doesn't recognize the file, either because it is corrupt or is missing the resource fork. My experience is that Norton is less successful in recovering program files completely (i.e. .rds, .ai, .fh, etc.) which require both forks of the file to be recognized as opposed to file formats like .tif or .jpg which may open with only the data fork intact. Norton sometimes recovers a program file without both forks intact (the data fork is there but the resource fork is not), even when it says it is 100% recoverable. Does the RDS icon show on the file? If not, you may be able to just re-add the creator/type codes using ResEdit or other program which adds creator and type codes. Sometimes opening the file from within the program as opposed to double clicking the icon works, but you probably already tried that. Also, rebuilding the desktop after a crash will occasionally make the file recognizable again. I wish I could be more helpful than that, but if none of these solutions work for me, I berate myself for not having a backup and accept that the file has been corrupted.