Uncaught TypeError: $(...).(thefuntionname) is not a function

Uncaught TypeError: $(...).(thefuntionname) is not a function

this is always the error i had in my website can someone help me. its already under a function({});. what should I do?

and sometimes even if theres an error the code still runs right.

the error : Uncaught TypeError: $(...).opacityrollover is not a function

the code:

Blockquote jQuery(document).ready(function($){ $('div.content').css('display', 'block');

            var onMouseOutOpacity = 0.67;
            $('#thumbs ul.thumbs li, div.navigation a.pageLink').opacityrollover({
                mouseOutOpacity:   onMouseOutOpacity,
                mouseOverOpacity:  1.0,
                fadeSpeed:         'fast',
                exemptionSelector: '.selected'
            });



    });

Blockquote