It looks like your gallery may be expanding on top of the embedding page.
Make sure you set expandInNewPage="TRUE" (in JuiceboxBuilder-Pro's 'Customize -> General' section) to ensure that the gallery always expands onto a new page of its own.
If this does not work, then maybe giving the gallery an opaque expandedBackgroundColor (any color with an opacity of 1) might help (in JuiceboxBuilder-Pro's 'Customize -> Color' section)
If this is not happening when the gallery is expanded (i.e. you are not using the Splash Page and the problem is seen when initially viewing your web page ), then the layout of your web page may be the key to solving the problem.
You can check the code on your web page (to see if there are perhaps any unclosed containers or, indeed, any other HTML related problems) using the W3C Markup Validation Service.
I hope this points you in the right direction.
However, if you continue to experience difficulties, then please post back with the URL to your gallery's web page so that I can see the problem for myself and hopefully help further.
Once I'm able to see the problem live on your web server, I should hopefully be able to determine the exact cause of hte problem and propose a solution.
Thank you.