How Do I Fix "Warning: call_user_func_array() expects parameter 2"?

We were getting this message in certain areas of Joomla when we would attempt to add a link or a picture to an article or module.

We noticed that the website in question did not have the latest version of Joomla installed. It used to be a pain to keep everything up to date. Not any more. We installed Admin Tools from Akeeba Backup on the Joomla websites in question. This didn't resolve the issue, but it's still a good thing to do first.

We use the JCE Content Editor for our Joomla websites. Downloading and installing the most recent version of the JCE content Editor seemed to resolve the issue.