Marketo Landing Page Giving Security Error After SSL Setup

Issue

After setting up SSL on a Marketo instance, some landing pages give a mixed content security warning.
 

Solution

This is usually caused by elements on the page that use "http" rather than "https" in the resource URL. To find the element, do the following:
  1. Open the landing page in the browser
  2. Right click on the page and select View Source from the menu
  3. When the source code is displayed, use "Ctrl+F" to find anything using "http" in the resource URL
  4. Make a note of the elements you find
  5. Open the Landing Page in the Landing Page editor and find the element
  6. Edit the HTML for the element by clicking on the "HTML" icon in the toolbar
  7. Change the "http" in the HTML to "https"