Screen display image matrix problem

1
Hi,
I am having a problem displaying an image matrix via both:

tex=Screen('MakeTexture', window, img);
Screen('DrawTextures',window, tex);

and just simply:

Screen(window,'PutImage',img);

I see a black box where the image should be.

The particular image is fine to write to a file via imwrite, and is also fine to see via imshow.
Any ideas?
Thanks,
Kurt