just out of curiosity, does this error persist after deactivating all plugins except nextgen? i know from my own experience, sometimes other plugins can cause features of another plugin to not work as well. this is the first thing i do when troubleshooting an error. also, are you up to date on wordpress?
@jonm173 - i can see the duplication on your site. @fightin498a, i'm not seeing the duplication on yours. did you find a solution?
i've heard that the plugin authors are introducing some pretty dramatic improvements to the code in v2.0, i bet that will help solve a lot of issues like this. as a temp. solution if you aren't able to find a fix to this (i haven't experienced this bug, so i don't know if i am being of much help), you could try using the plugin 'lightbox plus'. i love that plugin for lightbox effects.