constant message " your username or password is incorrect"

constant message " your username or password is incorrect"

I continue to get the above message from both my iphone and my windows live mail account, it comes and goes all the time, I have checked my un/pw and both are correct.

Basically, lets use my iphone for an example, if I open the mail it automatically checks for new mail, sometimes all is good others I get the message, if I get the message a few minutes later the mail will just show up and I get no errors