First of all, try re-uploading the plugin's files to ensure that they are all present and correct (just in case and files are missing or somehow became corrupt during the initial upload).

I notice that the problem occurs in your Flickr and NextGEN sourced galleries.
Do you have any Media Library galleries which you can test?

The problem is possibly due to a PHP function which WP-SimpleViewer uses which may be disabled in your web server's PHP configuration settings (or perhaps a bug in the PHP version installed on your web server). What version of PHP does your web server have installed?

I should be able to determine the cause of the problem if I had access to your web server.
If you are willing to allow me FTP access to your web space (I will leave things exactly as I find them), please let me know and I will send you an email address to send me your login details. Thank you.