"I am not able" is not a useful problem
description. It does not say what you did.
It does not say what happened when you did
it. As usual, a transcript showing actual
commands with their actual output can be more
helpful than vague descriptions or
interpretations. With my weak psychic
powers, guesswork follows.
> [...] any other user.
And these other users can log in
interactively with no trouble?
Who is using which shell?
man shells
> #man ftpd
And look for "shell".
