I was able to add photos to a blank GPX. However, you may be getting a bug that is in the latest version right now. It is fixed in the beta if you want to move to that.
Actually, you can avoid the bug simply by assigning a "HTML destination" directory at the bottom of the PhotoFusion form. As long as that isn't blank, it won't give you the error / crash. Sorry about that issue, it was introduced inadvertently in the last update.