Your problem arises since your function_form output is different for IE8 and other browsers. In IE you get response like this one (error 500 which is html):
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>500 Internal Server Error</title>
</head><body>
<h1>Internal Server Error</h1>
<p>The server encountered an internal error or
misconfiguration and was unable to complete
your request.</p>
<p>Please contact the server administrator,
root@localhost and inform them of the time the error occurred,
and anything you might have done that may have
caused the error.</p>
<p>More information about this error may be available
in the server error log.</p>
<hr>
<address>Apache/2.2.15 (CentOS) Server at carlyleonline.scalahed.com Port 80</address>
</body></html>
and then it fails with:
var datas = $.parseJSON(data.responseText);
Other browsers on the other hand return proper JSON:
{"errores": {"entidad": ["Este campo es obligatorio."], "fecha_nacimiento": ["Este campo es obligatorio."], "apellido_paterno": ["Este campo es obligatorio."], "carlyle_lic1": ["Seleccione al menos una licenciatura."], "celular": ["Proporcione un n\u00famero telef\u00f3nico."], "nombre": ["Este campo es obligatorio."], "email": ["Este campo es obligatorio."]}}
Can you show us your logic which determines if response should be json or webserver error?