WYSIWYG editor not showing when large html content edited

when trying to edit a large html comntent, the wysisyg editor dissapears insteas getting the html code
looking in the broweser console:
http://wdev.sapir.ac.il/misc/jquery.js?v=1.4.4 Failed to load resource: the server responded with a status of 413 (Request Entity Too Large)c.extend.ajax @ jquery.js?v=1.4.4:142