Problem with disallowed key characters when i send a photo(bytes)

[eluser]Unknown[/eluser]
Hello, I had problem when I send a photo in bytes. I have a ajax that find a photo:

function crea_evento(){
$( "#dialog-confirm-evento" ).dialog({
resizable: false,
height:140,
modal: true,
buttons: {
"Si": function() {
$( this ).dialog( "close" );
//alert(readBlob();

var files = document.getElementById('files').files;
if (!files.length) {
alert('Please select a file!');
return;
}

var file = files[0];
var start = 0;
var stop = file.size - 1;

var reader = new FileReader();

var foto = evt.target.result;

foto = (foto + '').replace(/[\\"']/g, '\\$&').replace(/\u0000/g, '\\0');
var parametros = '{'+'"f": + foto + '}';
$.ajax({
//url: "web/control_evento/registro_evento",
url: "web/control_evento/registro_evento",
type: "POST",
data: parametros,
dataType: 'html',
success: function(data){
$( this ).dialog( "close" );
init_evento();

var obj = jQuery.parseJSON(data);
var merror = obj.me;
alert("me : " + merror);
}
});
};

if (file.webkitSlice) {
var blob = file.webkitSlice(start, stop + 1);
} else if (file.mozSlice) {
var blob = file.mozSlice(start, stop + 1);
}
reader.readAsBinaryString(blob);



},
"No": function() {
$( this ).dialog( "close" );

}
}
});
}

The error is Disallowed Key Characters.

Please Help me!!!!!!!!