[SOLVED] Thumbnail Cropping Not Working

Using Wordpress 3.5.2 and Atahualpa 3.7.12, with plugins including Post-Page Associator.

When I load a long, narrow picture of a person (full body) in a post, the excerpt of the post generated by Post-Page Associator shows a thumbnail with the person's head cut off.

In trying to fix this, I went to Media Library, and tried to Edit and Crop just the thumbnail of the original photo. However, after Cropping, when I click "Save" below the cropping screen, nothing happens. When I clicked "Update" (in the right column on the edit photo page), it appears to Save, but no change is made to the thumbnail, and the problem persists.

I want the full post to show the full-length image of the person (so am not selecting Thumbnail size when uploading the image to the post). But, I want the thumbnail in the excerpt of the post generated on a page of the site by Post-Page Associator to be cropped so that it will show the head of the person.

How to fix this?

Many thanks in advance for any help.