Failed to load resource: the server responded with a status of 500 (Internal Server Error)

Failed to load resource: the server responded with a status of 500 (Internal Server Error)

I get an error when  I make lots of post's requests to the server, and Jquery doesnt return all the values. The erros says:
Failed to load resource: the server responded with a status of 500 (Internal Server Error) , 
and the code I'm using is:

$.ajax({ url: "serv_banners.php", type: "POST", data: "serv=banner_izq_inf", success: function(datos){ $("#banner_izq_inf").empty(); $("#banner_izq_inf").html(datos); } });