DataTables: Cannot read property 'length' of undefined

Question

I understand this a popular issue, and I have read all the similar questions here on Stack Overflow and other sites (including the datatables website).

To clarify, I

Answer 1

While the above answers describe the situation well, while troubleshooting the issue check also that browser really gets the format DataTables expects. There maybe other reasons not to get the data. For example, if the user does not have access to the data URL and gets some HTML instead. Or the remote system has some unfortunate "fix-ups" in place. Network tab in the browser's Debug tools helps.