TypeError: j(...).bxSlider is not a function - Sliders are not working

After trying lots of different things, I've managed to solve my own problem. I've put the JavaScript files for bxSlider, easyResponsiveTabs and the scripts calling them to footer.php. But I've left the jQuery & jQuery UI files at the header.php along with the css files for the sliders.

Now everything is working well and the markup passed the validation test!If you're having same kind of error;

1. Check your jQuery and other JavaScript file paths.
2. Check if you're using an old version of jQuery or incompatible versions of jQuery & jQuery UI.
3. Don't work with stupid developers that may put all your link tags to footer.php and call the scripts from header.php...
4. Check if you have different instances and/or versions of jquery.min.js
5. (In my situation) Put your bxSlider js files to footer.php but leave the css files in header.php (for validation, just this way it worked well)

Also you can write to me, I can try to help.

Most likely the cause is multiple instances of jQuery. Look further down in your , you'll see that WP has inserted more tags, one of which looks to be jQuery.

The second instance of jQuery is probably being inserted by a plugin. Try to identify which and disable to see if it fixes the problem.

Some people answer that check the jQuery scripts, make sure only have one. But not answer to the "why?" question. I had the same (this question) problem, but resolved. The bxSlider's (linked) JS file make a function to the jQuery, and a later file overwrite this function (delete it, because jQuery don't contain the bxSlider stuff originally). So the answer: put the JS linking after the last jQuery JS file linking, and then works.