Illustrator :: Rectangle Missing In Save To Web?

I'm using Illustrator CS4 at work and am rather new to it, so I'm feeling my way along. I'm modifying and working with a file created by someone else. I'm trying to save a document of multiple objects to JPG, using Save to Web & Devices. There's a white rectangle in the document that I can't seem to include in the saved file. Other objects are included without problem, both clipping to the artboard and saving the whole document. I've tried grouping the rectangle with similar adjacent objects, and also tried "locking" them. I even tried creating a new rectangle over top of the existing one. No matter what I try, it just won't grab that rectangle along with the rest of the objects. It doesn't seem to be in a separate layer.