I'm running GImp 2.6.11 on Mac OS 10.4.11.
I took an image, rotated it and then cropped it. When I selected Smart Enlarge from the Enhance menu, Smart Enlarge was grey and inactive. I tried selecting the image in several ways but that did not work.
However, another image that I did not rotate and crop gave no trouble with Smart Enlarge. That is, Smart Enlarge was active and worked.
Thank you for your help.