WP-SimpleViewer v22.214.171.124 requires PHP v5.2.0 or later so should work fine with v5.4.28.
Perhaps WP-SimpleViewer v126.96.36.199 uses a PHP function which has been disabled in your web server's PHP configuration settings.
WP-SimpleViewer supports several different image sources for galleries (Media Library, Flickr Account, NextGEN Gallery, Picasa Web Album).
Does the problem occur with all image sources of just one?
If you have currently been using only the Media Library, try using a different image source (just for testing purposes) to see if the problem still occurs.
If you do not have a Flickr account or a Picasa Web Album to test, try the following details:
Flickr Username: [leave this entry blank]
Flickr Tags: [leave this entry blank]
Picasa User Id: picasateam
Picasa Album Name: VegasWeekend
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.
SimpleViewer Support Team.