What happened? Used a D70 Nikon, camera? photo program? corrupt? Pls give me some advice, I need it.

It doesn't look corrupt, more like the shutter is faulty.
The line across the image is sharp, that means it's not the mirror sticking which is a long way from the sensor. More likely to be the shutter if it works vertically on that camera.

Odd. My first thoughts are the shutter curtain as well. Since the bottom is exposed and not completely black, it looks like the shutter stuttered.

Question: does this happen often? does it happen at a particular shutter speed?

I would say this only happens on about 1 out of every 150 to 200 pictures. I wasn't sure if ACDSee caused the problem or what. I have even noticed photos I scanned in many years ago getting this darker look... I have even seen it shift the photo as well. See another example attached of a shift...

Now this one is definitely NOT an optical/mechanical issue. A software (either in-camera or uploader) for sure.

I can't say which and why. I would advise posting these two images in the Help forum. I too would like to see what is causing this.

Film wasn't so bad was it :rolleyes:

Now this second example is definitely a file issue.
See how part of the image is moved to the right?

Either this is your old scanning software and your new image viewing software not agreeing on how the file should be formatted. Or it's a corruption of the file on the disk.

Usually with a corruption I find that part of the image is overlaid on the rest of the image, and it affects only one or two colour planes (red, green or blue) and not all of them. But the effect of this kind of problem is so random that it's hard to diagnose.

The reason I suspected the camera and not the software or the file was that there was no vertical or horizontal shifting in the alligator image, just the darkening.