I figured it out, but I want to post this to help others.
If you are using Simple Image Gallery on the same page of RIE 1.7, and you aren't using the same lightbox style, i.e. Slimbox, Shadowbox, and Milkbox, as your Simple Image Gallery lightbox style the following may/will occur:
When you click to enlarge an image in the SIG, it will open 2 lightboxes. First, the RIE style, then the SIG style on top of it. The browser will then need to X out of both of the images.
To remedy, make sure your RIE style matches. For me, I selected the Slimbox style and it only opened one larger image for the SIG image clicked.