Hi Mahendra,
As an initial check, verify whether you have checked the BEx Query property within the checkbox 'Allow external access to query'. Even if you face the error confirm whether the password for SAP user is same i.e. it has not expired else you need to reset the password and reuse the new password for login. If still you face the error then you may try to restart your web application server once and check thereafter. Hope this helps.
Rgds,
Ray