It seems like no one, not even the original reporter, is able to reproduce the error.
From what it seems like from the error and the following discussions, the table was instantiated during the first draw of the page, before the DOM was ready. Then, perhaps the $().ready executed when the DOM was ready, and tried to instantiate the table. This seems like a flaw in the underlying datatables code, if it is unable to respond in a friendly way when the table is already ready. However, since the datatables script is minified, it is not in our ability to look into this theory, since only the datatables author has the unminified code. Although it is not clear why the script attempted to run twice, the author may have already fixed the issue on your site, since no one has been able to reproduce it.
If you had been using some kind of optimize script that moves Javascript to the end of the HTML, such a script might cause problems like this. Optimize scripts need to provide some way for other scripts to opt out. Then other scripts need to be aware of the opt-out procedure in order to do so.
Marking this as Cannot Reproduce for now. If this issue returns, you will need to start with the datatables author because they will be able to trace through their minified code and see what is happening.