$.ajaxq is not a function

I am having a bit of problem with Market Press, add to cart functionality. When I click to "Add to Cart" I get:

$.ajaxq is not a function
    at Object.mp_cart.addItem (mp-cart.js:414)
    at HTMLFormElement.<anonymous> (mp-cart.js:90)
    at HTMLElement.dispatch (7f7b3a78419549f7d9e028ceaef2b689.js:3)
    at HTMLElement.m.handle (7f7b3a78419549f7d9e028ceaef2b689.js:3)

Hummingbird Plugin is on.

Thank you in advance.