Yes, I paid attention when mounting the lens and hear the click every time. As said the "bad" lens works fine on the D40 but not on the D3000. I also mounted the lens on a film camera F60, although I can't take pictures due to no film but the objects seen thru the viewfinder are at least clear and bright as with the eyesight, while on the D3000, the objects thru the viewfinder are as dark as come out in the pictures.

the situation:
D3000 with other lens OK
"bad" lens with other cameras OK
D3000 with "bad" lens deliver very dark pictures.

Thanks!