PNG files get unlinked and become all yellow/negative

I am making some catalogue and when I import files all is fine. PNG files with removed white background (classic product images). While I am working everything is ok, but when I shut down Illustrator and computer, after I start working again the images are all yellow and looking like something like a film negative. PNG images are 8bit , exported from Photoshop. 

Now I have to relink them one by one which is not the thing I want to do since there is a lot of images.
Anybody had this problem and is there a solution for preventing this?
Image is attached.

Thanks!