MumblingFumbler on "Portrait Images are not sized/displayed"

3672 x 4896 px jpg images are not getting sized/displayed in Zenphoto album. 4896 x 3672 (landscape) are displayed fine.
Absolute jpg file size is not the problem, since larger jpg files are displayed correctly. I read the troubleshooting posts display problems with large image files. Debug information didn't reveal any error in the image. Tried switching to Image Magick engine, but that caused a whole lot of problems (caused multiple setup invocations and a bunch of errors), and was very slow, although some of the previously erroneous images were properly sized/displayed--switched back to GD. Can I set script maximum memory to higher than 128M in php.ini? Thanks for any suggestions.