As I already answered in the email, there should be some PHP error occurred. To investigate it we need to know that error.
When your site is handling some operations, which are not succeed, the webserver (environment in which your site is working) will write resulting error messages somewhere on the disk.
In case of WordPress (and many other PHP sites) this error file may be called error_log and may be placed in the site root near the wp-config.php file of your WordPress installation.
To help you fix the issue we’ll need to know what error messages appeared after you try to use the PDF Light Viewer plugin.
