ACS Invalid Request error with no log in the managment console

I am trying to store some data on Custom Object of Appcelerator ACS. So there will be a service to do that. Each time it require authentication to create a new object

But I am sometime getting below error while login with ACS. But it not occuring always. It only if I call service multiple time.

error i am getting is:

{ success: false, error: true, code: 400, message: "Invalid request sent." }

Code used to login :

ACS.Users.login(userData, function(data){
if(data.success)

{ console.log("----------Successful to login.---------------"); console.log(data); res.send(data); res.end(); }

else

{ console.log("------------------login failed---------------"); console.log(data); res.send(data); res.end(); }

},req, res);
Can some one can help me to understand how to re-use session id from node.ACS web service app (Not web app)?

How I can keep session / check session validity before pushing something to custom object? Has anyone faced similar issue?

Thanks
Peter