An unknown or invalid jpeg marker is found

Question

"an unknown or invalid jpeg marker is found"
jpegs being corrupted when copied
Each one, in different folders, copied from my MacBookPro’s desk top, all rendered out as a full sized jpeg, 300dpi, but then when I transfer them onto another HD, they all render out as the correct MB size (12MB etc), but they are sized 256 x 171 in the Bridge Info panel and none will open in Preview or Bridge or Photoshop, “Could not complete your request as an unknown or invalid jpeg marker is found"
They worked fine originally. Other files etc work well on the HD. i do not use anything other than jpeg and the original RAW files so all extensions are correct.
Thanks

Answer 1

You are correct in that this particular message means your files are hosed.
Your external HD could be going south, or the connection may be faulty, check all cable ends, the computer ports, etc.
How are you "transferring" them?  That's a term that gives me hives.