Randomly, it stop working

Hi there
someone else happend that randomly the tabs stop working?
it simply shows the list item instead of the tabs
this is the second time this happend to me, the first time, it fix alone in a hours
any idea of what it can be?
i suspect of a external file wich it cant be leaded, but cant figure out wich one
thanks in advance

http://wordpress.org/extend/plugins/wordpress-post-tabs/