This problem happens with jQuery Easing Plugin. This error occurs when a newer version of jquery and jquery.easing is used with an older version of the call to animate.easing.
Use the following jQuery, JQuery Easing and JQuery Easing Compatibility
Download JQuery – Latest version from JQuery
Download JQuery – Version 1.5.2 hosted at Google
JQuery Easing Plugin – Version 1.3 by George McGinley Smith
JQuery Easing Compatibility (for use with older versions) – by George McGinley Smith