I just figured it out: You MUST have enableviewstate="true" on the insertgallery.aspx page if you have enableviewstate="false" in your web.config files (for performance reasons) like I did.

May want to mention that in your documentation.   If enableviewstate is equal to false, the image gallery pop-up will fail with the object error message described in my earlier post.

Now, my only other question is How can I specify to automatically rename thumbnails to someimage_thumb.jpg or someimage_thumb.gif? The thumbnail creator adds t___ to the prefix which we need to change.

Thanks for checking into this.

Chris