Amazon S3 not working properly on first upload request but working on second

I am using Amazon S3 webservice to upload my file.

        var req = bucket.putObject(params).on('httpUploadProgress', function (progress) {
            ....some action
        }).send(function (err, data) {
            console.log(err);
            ....some action
        });

When I execute the above operation it gives me following error.

Error: No credentials to load
at i (http://ift.tt/1GQkIHO)
at i.a [as getCredentials] (http://ift.tt/1QVj53i)
at a.u (http://ift.tt/1GQkIHQ)
at a.h [as callListeners] (http://ift.tt/1QVj3bD)
at a.l (http://ift.tt/1GQkIY4)
at a.v (http://ift.tt/1QVj53k)
at a.n (http://ift.tt/1QVj53m)
at n.i [as runTo] (http://ift.tt/1GQkJvj)
at http://ift.tt/1QVj3bF
at a.<anonymous> (http://ift.tt/1QVj3bH)

When I again click on same button which execute the above, this time it works properly. What is the issue here