Invalid User Name or Password, try again.

i have AccessToken and appId am trying this authorization for a seller. using link below i've given my return url and appID in the url below
" https://stg-authorize.snapdeal.com/authserverui/login?returnURL={RETURN_URL}&appId={REGISTERED EMAIL ID OF PARTNER} "

then entered snapdeal sellercredential but it throes error as
" Invalid User Name or Password, try again."

NOTE: using the same credential i can login to seller.snapdeal.com but while authorization it throws error for the same credential.

why ????