Never encountered this bug. The only criterion for that message is that the ImageGalleryPage has no ID. So you might want to verify in your database that it does have a valid RootFolder. For some reason it's not able to create assets/image-gallery/MyGalleryPageName.
1) That there is an "image-gallery" folder as an immediate descendant of "assets."
2) That there is a folder named after your ImageGalleryPage Title as an immediate descendant of "image-gallery"
3) That there is a "Default-Album" folder that immediately descends the folder named after your ImageGalleryPage.