signin problem

When I open windows messenger it shows my email address and tries to sign in
automatically. But it always comes back with an error message saying that
either my email or password is incorrect. If I then click to sign in as
another user and I put in the exact same email address and then type in my
password , I then get messenger started ok. Does anyone have any idea as to
why the sutomatic start up always kicks out as an error? Thanks.
Carl