Maybe it's a corrupt preference file. You could try recreating it - it'll mean reconfiguring it the way you like it, but it might work.
Click on the Desktop and hold down the option/alt key and from the Go Menu select Library>Preferences and find this file:
Move it to the desktop (so that you can put it back if this makes no difference) and restart and it should create a new preference using the defaults. Check to see if it's made a difference.
I think the problem is solved
When I delete the files from the downloads folder... the problem is not solved.
Later when I wanted to delete files permanently from the trash, a message appeared:
"X file can not be deleted because it is being used"
(it was a big size file about 2gb)
When I finally unlock the file and delete it from the trash, the icons were recovering their pictures in all affected folders
Somehow it seems that the file interfered with the icons
I hope it does not happen again
Thanks to all