In Moodle, why is a particular page blank or incomplete?

Does this happen when trying to open a PDF resource?

This issue may occur when a user tries to open a PDF resource due to an incompatibility between Moodle and the Adobe Reader plugin on some of the most recent browsers. Generally speaking, refreshing the window (clicking the Refresh/Reload button, or pressing F5) will eventually bring up the PDF, though sometimes it takes two or three tries. This quickly becomes annoying to the user. To resolve the problem, select the “Force download” option in the resource settings when posting a PDF.

We also recommend updating your browser and Adobe Reader plugin to the latest version in order to optimize compatibility.

If this is not a PDF display issue, it may indicate that an error has occurred when Moodle is trying to display a page. Please let you system administrator know about the problem.

(Details for system admins: Depending on the server’s configuration, PHP might hide error messages. If this is the case, when an error in a PHP script occurs, PHP might choose to not display anything, resulting in a blank page.

Usually, PHP should not display error messages in a web page for security reasons. However, there are exceptions, e.g. when you are debugging a web page.

To globally enable error messag display, put these in your php.ini file:
display_errors = On
error_reporting = E_ERROR

To enable that for a single PHP script, put these at the beginning of the script:
ini_set(‘display_errors’, 1);

See the Moodle FAQ for details.)