AWS.S3 in some point doesn't execute callback

we use node.js and S3.

I have the following code to check if a file is exists:

var s3 = new AWS.S3();

S3.prototype.search = function (baseDirectory, url, size, callBack) {
           console.log("we are in the correct function");
            s3.headObject({"Key" : url.substring(1, url.length), "Bucket" : S3_BUCKET}, function (err, data) {
                console.log("Callback is done");

        })}

Everything works O.K, but in some point I notice that the callback is not return. Meaning, I get only:

  console.log("we are in the correct function");

But "Callback is done" isn't printed.

What can be the reason for this?