So, does anyone have any answers to the initial post?
I have just started trying to use the gallery, and I am having the same problem (though I am not using the image grid plugin as the op is).
I have uninstalled and reinstalled.
I get an error message in each case saying that the memory limit has been exceeded, and that 93 mb of memory (!!?) is required.
My images are between 1 and 2 mb jpg files.
Thoughts?