Using the jQuery library, I get an error in the jquery file.

Using the jQuery library, I get an error in the jquery file.

We are trying to do some effects, and work properly in Firefox and Chrome but not in IE, loading the page everything is ok, but when I click the ID for me to run the function, get error.
 
Detalles de error de página web
Agente de usuario: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; .NET4.0C; .NET4.0E)
Fecha: Sun, 13 Mar 2011 03:39:17 UTC

Mensaje: No se pudo obtener la propiedad position . Argumento no válido.
Línea: 7909
Carácter: 5
Código: 0
URI:



 http://localhost:8080/movigroup/jquery-1.5.1.js
 
 Any ideas?
My code is as follows:
  1. $("#navigate1").click(function(e){
       e.preventDefault()
       var lesser = $("#idreturn").text();
       if(lesser == "BIENVENIDA"){
        $("#idreturn").html("<span class='idreturn'>BIENVENIDA</span><span class='enlacenow'> / DESCARGAS</span>");
       };
       $("#nav2").css({'position':"absolute",'width': "0px",'overflow': "hidden",'z-index' :"1000"});
       $("#nav3").css({'position':"absolute",'width': "0px",'overflow': "hidden",'z-index' :"1000"});
       var n = $('#nav1').width();
       if( n ==0){
        $("#nav1").animate({
         'position' : 'relative',
         'width': "+=692px",
         'overflow' : "visible",
         'z-index' : "20000"
        });
       };
      });
















    Thanks