I read this on the Nextgen site.
What helps after migrating your site from one location to the new location is running the NextGEN Reset Tool. This is located under Gallery > Other Options > Reset Options. Running this tool will not cause you to lose your galleries. What it does is clear any stored cache (i.e. old site URLs) and restores the global gallery settings back to default. So you will need to go back and re-adjust those settings after running the reset, but this tool may resolve the issue you’re seeing with the lightbox.
Hope this is your answer.
