Try downloading the latest version of WP-SimpleViewer (v2.3.2.5) directly from the plugin's support page here.
Then, manually install the plugin on top of the existing version by following the installation instructions here.
This should ensure that all the plugin's files are present and correct.
If you are in any doubt as to whether or not the existing files on your web server are being overwritten, then try deleting the existing 'wp-simpleviewer' folder from your plugin directory first before uploading the fresh version of the plugin in its place.

If this does not help, then please post the URL to one of your gallery's that displays the error message so that I can see the problem for myself and hopefully help further. Thank you.

Thank you for providing the links to your galleries.

Your gallery XML files in the 'wp-content/uploads/' directory do not seem to have all the necessary configuration options required for the 'config.php' file to dynamically build an XML file when a gallery is viewed.
Do you remember what version of WP-SimpleViewer you used to create your galleries?

Try going to the 'SimpleViewer -> Manage Galleries' page from the WordPress Dashboard and edit each of your existing galleries.
Just click 'Edit Gallery' and then click the 'Save' button for each one without actually making any changes.
This should hopefully help.

I'm really not sure what might have caused your problem but the fact that certain required configuration options were missing from you gallery XML files seems rather strange (and, as far as I can remember, I've not seen it before).

Re-saving your galleries seems to have reinstated the missing configuration options (I now see them in your gallery XML files) but I notice that your galleries still do not display.

It looks like there might be a problem with the plugin's 'config.php' file on your web server.
The file might be corrupt or incomplete or the script might use a PHP function which is unavailable or disabled on your web hosting account. (WP-SimpleViewer requires PHP v5.2.0 or later.)

It sounds like you have already tried re-installing the plugin so I'm not sure what to suggest next.
I would be happy to investigate further but, in order to do so, it would help if I had access to your web server and WordPress site.
If you are agreeable to this, then please let me know and I will send you an email address where you can forward me your FTP login details (host, username and password) and WordPress login details (URL, username and password). Once I have access to the WP-SimpleViewer files on your web server, I should hopefully be able to determine the cause of the problem and propose a fix or workaround.
Thank you.

Thank you for checking your web server's PHP version.
WP-SimpleViewer should run fine on PHP v5.4.

Please check your email. I have sent you a message.
Thank you.

Please check your email. I have sent you another message.
It looks like your Block Bad Queries plugin has been preventing the include_once instructions from running in the 'wp_simpleviewer/config.php' file resulting in required functionality not being available (breaking WP-SimpleViewer).
I hope this helps.