Preview not working

I added the Equation Editor through a custom CKEditor 4.7.3 build. Overall the plugin is working fine (dialog appears, hitting ok inserts it into the content), but the Preview isn't working. Whenever the equation is updated, the following error appears in the console for the file "eq_editor-lite-17.js":

Uncaught TypeError: Cannot set property 'src' of null at EqTextArea.renderEqn (eq_editor-lite-17.js:1) at EqTextArea.renderCountdown (eq_editor-lite-17.js:1) at EqTextArea.renderCountdown (eq_editor-lite-17.js:1) at EqTextArea.renderCountdown (eq_editor-lite-17.js:1) at EqTextArea.renderCountdown (eq_editor-lite-17.js:1) at EqTextArea.renderCountdown (eq_editor-lite-17.js:1) at EqTextArea.renderCountdown (eq_editor-lite-17.js:1) at EqTextArea.renderCountdown (eq_editor-lite-17.js:1) at EqTextArea.renderCountdown (eq_editor-lite-17.js:1) at EqTextArea.renderCountdown (eq_editor-lite-17.js:1)

Is this a known issue, or something I'll need to debug on my install?

thanks