Double-check that Adobe Flash Player is installed in your browser by visiting this web page: https://helpx.adobe.com/flash-player.html
Also, make sure that the useFlash Embed Code Parameter is set to TRUE in your gallery's embedding code.
If useFlash is TRUE, SimpleViewer will display the gallery using the Flash Player (if available in the browser), falling back to the Mobile Player if Adobe Flash Player is unavailable.
If useFlash is FALSE, SimpleViewer will use the Mobile Player to display the gallery regardless of whether or not Adobe Flash Player is installed and enabled in the browser.
You might like to try viewing your gallery in a different browser (Chrome, Firefox, Opera, Safari) to see if the problem is somehow unique to your default browser.
1. Open Gallery looks good in Customize view. When Flash check is on, the Gallery/Preview displays the background color with a white strip in the center.
It sounds like the FAQ below might help (especially if you are embedding your gallery in a web page alongside other content rather than just viewing the gallery on its own 'index.html's page as generated by svBuilder-Pro).
My gallery does not show in Firefox or gets cropped to a small height. Why?
A quick and easy solution to this problem (if you are currently using a gallery height of 100%) is to give your gallery a fixed height (such as '600px') instead.
2. When Flash is unchecked, it displays a grid of unformatted thumbnails.
This sounds normal (though I am not sure what you mean by 'unformatted').
Please see these FAQs:
When I view my gallery I see a grid of thumbnails, not the layout I specified. Why?
The mobile player layout does not match the Flash player layout. Why not?
If you continue to experience difficulties, please post the URL to your gallery's web page (so that I can take a look for myself) and, if possible, please upload a screenshot somewhere (either to your own website or a file sharing service like Dropbox) so that I can see what you are seeing.
SimpleViewer Support Team