diego_circo on "[Plugin: Contact Form 7] No confirmation after sending"

After sending the form.
The mail already sent but no confirmation and the looping arrows moving in circles.
I inspect and here the result

TypeError: $.isPlainObject is not a function
[Parar en este error]

if (! $.isPlainObject(data) || $.isEmptyObject(data))

Anyone know the solution?
Thanks

http://wordpress.org/extend/plugins/contact-form-7/