White options screen (NOT white screen of death)

This is not a completely white screen, which would indicate an error, this is just blank options, everything else can be seen correctly.

Unfortunately, this seems to happen to a number of our websites.
The website where we have installed the plugin is an existing site that has been redesigned and all files replaced. We already have an account and I have generated a new php file from your website, but there is no way to add my details.
I checked the source coding and found that it is completely blank, no text or anything else is being generated on this page where your plugin details should show.

Our server is using the latest stable release of everything as it is updated regularly.
WordPress is also using the latest version and all plugins are updated. I switched on debug mode and could not see anything that related to your plugin.

view screenshot

Please let me know if you need anything else.

Many thanks
Dave

http://wordpress.org/extend/plugins/websitedefender-wordpress-security/