I want to choose an image from my gallery to be the representative thumbnail. However, when I go into the drop down menu to select an image I'm only given the first 10 images (out of a total 64) to choose from. How do I select one of the other 54 images not in the list?

You should be gettin all the images listed. Check to see if you have got some kind of CGI error. Also Check to see what the name & title of the 11th image is. Perhaps it is causing problems.