I have found the culprit 
changing extension to .zip of the .gwd file, extracted everything in a new folder, one of the images a .png file (a battery bar) was not showing anything in Photo Viewer.
changed extension back from .zip to .gwd, opened it in GWS, deleted the image, added it again, error message still appeared when opening the .gwd file, changed .gwd again to .zip opened the .zip file with WinRAR removed the damaged .png file from /res folder changed the .zip back to .gwd and opened the .gwd file again in GWS, no more error message
posted it here maybe it will help someone else
Thanks again for the suggestions, i can continue my work now with a new face 
P.S. “damaged” file, i think, it was added from a .psd file