If you're seeing a "cannot save, 500 error message, internal server error," when you try to save, or content is not loading or appears blank, try clearing your browser's cache and cookies.
Anti-virus software could also be the cause of these errors. Please check with your anti-virus provider to see how to add ck12.org to their list of supported websites.
Browser plugins can also cause errors to occur. One known plugin is the Ginger spell checker. This plugin can cause save failures if *.ck12.org is not added to the Disable Ginger in these websites: section in the settings for the plugin.