How do i fix 'Error on page'
 

On every page on my forum including the adminCP i get 'Error on page' at the bottom of the browser.

This is something to do with javascript.

when i double click that Error on page at the bottom of the browser it shows the line of the error. and this is the line of the error..

<!--
// Main vBulletin Javascript Initialization
vBulletin_init();
//-->

how can i fix this?