Sigo con la validación y ahora me da un error de sintaxis en el javascript  que he modificado.

 ¿A que puede ser debido este error? Muchas gracias  
 Código PHP:
    <script language="JavaScript">
 
function verificarfacturacion (){
    
    numero =document.formulario.txtdomicilio.value;
    let = dni.substr(dni.length-1,1);
    numero = numero % 23;
    letra='TRWAGMYFPDXBNJZSQVHLCKET';
    letra=letra.substring(numero,numero+1);
    
    if (document.formulario.txtnombre.value == ""){
        document.formulario.txtnombre.focus();
        alert("Introduce el nombre o razón social ");
        }
    
        else{
            if (document.formulario.txtdomicilio.value==""){
                document.formulario.txtdomicilio.focus();
                alert("Introduce el domicilio:.");
                }
                else{
                    if (document.formulario.txtcp.value==""){
                        document.formulario.txtcp.focus();
                        alert("Introduce el código postal");
                        }
                        else{
                            if (document.formulario.txtlocalidad.value==""){
                                document.formulario.txtlocalidad.focus();
                                alert("Introduce la localidad");
                                }
                                else{                                    
                                    if (document.formulario.txtcif.value==""){
                                        document.formulario.txtcif.focus();
                                        alert("Introduce el CIF/NIF");
                                        }
                                        var ubicacion
                                        var enter = "\n"
                                        var caracteres = "abcdefghijklmnopqrstuvwxyzñ1234567890"+ String.fromCharCode(13) + enter + caract_extra
                                        var contador=0 
                                        for (var i=0; i <document.formulario.txtcif.lenght; i++){
                                            ubicacion=document.formulario.txtcif.substring(i,i +1)
                                            if (caracteres.indexOf(ubicacion) != -1){
                                                contador++
                                            }else{
                                                alert("Error: No se acepta el caracter '" + ubicacion + "'.")                                            
                                            }                                        
                                        }
                                    }
                                else{                                    
                                    if (document.formulario.txtcfactura.value==""){
                                        document.formulario.txtcfactura.focus();
                                        alert("Introduce el concepto factura");
                                        }
                                        else{
                                            if (document.formulario.txtbimpon.value==""){
                                                document.formulario.txtbimpon.focus();
                                                alert("Introduce la base imponible ");
                                                }
                                                else{                                    
                                                    return (true);
                                                }                                            
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
        
        
    return (false);
 
}
                
 
</script>