Whats causing this data loss (if thats what it is)

When the motherboard on my old computer died,I bought a new computer and added a 500gig external drive to it. When I put the drive from my old computer into an external case and copied the files, I sent them directly to the new external drive. Shortly afterwards, when I would open them in Adobe bridge, they would start doing what yours did one by one.
I finally deleted them from the external drive and copied straight to the new computer and then to the new external drive and the problem was solved. No clue why though.

Does this happen permanently, that is once messed up, it stays messed up? If so then RAM is not the problem unless you then write out the corrupted file. My guess is that header info is getting corrupted on your external drive. Time to go pull the pic from your backup. You might want to check other pics as well. Also doing a full disk scan of your external drive might uncover other issues as well.

Yes its permanent... Could you elaborate a little on what you mean gjl711??? Also do you recommend any good HDD scanners?

If the file is corrupted because of a RAM issue, it would be different every time you load it so clearly the corruption is farther upstream. If the corruption is due to poor data transfer, again the data would be different every time you download so that leaves the hard drive itself. Data can get corrupted on the drive. When the picture is loaded it will look the same each time as the data corruption is now par of the file. If the files are damaged, the only way you’re going to get the data back is pull it from your backup pics and overwrite the bad file(s) on your external drive.

You can run a disk scan (chkdsk) and it will do some simple checks for data/directory integrity and may find and correct other issues as well. It’s not a bad thing to do periodically just to make sure your hard drives are behaving as expected. It does take quite some time to run depending on the size of your hard drive and what checks you enable before running it. Check out this MS link for more details.
http://support.microso​ft.com/kb/315265

kcbrown wrote in post #4168999
the reason I'm reluctant to suspect the drive is that the drive has error correction built into the way it stores data. When it detects any corruption in a block, it remaps the bad blocks to different areas of the disk transparently so that it can continue to function. If your image were corrupt in that fashion (which would only happen if the error in question was detectable but uncorrectable) you'd see the "bad" portion of it as completely missing. I don't know if there's a similar amount of error correction happening on the bus (USB or firewire, depending on what you're using) but I wouldn't be surprised if there is. The chance of an undetectable error happening on the drive is very, very low -- low enough that I could maybe see it happening once to one of your images like this, but not more than once.

Well, not quite. Yes, most drives today will move the bad block, but if the block wasn't read correctly to start with as it was copied.....

And yes, it does happen. Since it's external, could be the cable or anything else along the line that's the source of the problem.

If it's a USB drive, are you powering the drive thru USB? If so, I'd stop and use a wall-wart to plug the drive into and power it. If it's a case of "once corrupt - always corrupt", especially at the same location in the image (doesn't move up or down, unless it only gets worse over time), then I'd strongly suspect the drive or cabling to the drive. I'd also consider where the USB cable is routed. Does it go over any other AC line? Does it go near a fluorescent light? Is it near something that uses a motor? Any of those can create an inductance in the cable, twiddling bits at inopportune times. Re-route the cable (or move the other offending articles), or invest in a better shielded USB cable (although I suspect that none truly exist).

Just thought I would share my experience (which is not with computers, but is with image files.

The image file is corrupted and if it is repeatable it is permanent corruption (this is why I keep a DVD backup and a hardrive backup)

Most likely causes of the corruption was during the transfer of the file to the external hradrive, second most likely was a corruption of the file while on the harddrive by other means.

I will let the more experienced computer folks provide the techical details.

The reason the error appears as it does is mostly due to the way jpeg compresses and then reads the data, it is far less likely to see this error in anyother format.

Just my experience,