Mootools Error when saving a page

I am getting the following error in my firebug console when I try to save a page after editing it. Specifically i am trying to link to a pdf when the error occurs.

Here’s what the console says:
($(B) || document).getElement is not a function
error source line: [Break on this error] case"!=":return(G!=D);case"~=":return ...return($(B)||document).getElement(A);

And here’s the line from the mootools.js that it is referring to:
case"!=":return(G!=D);case"~=":return G.contains(D," ");}return false;});return(E)?C:new Elements(C);}});function $E(A,B){return($(B)||document).getElement(A);

Any help would be greatly appreciated