Unable to set up account on my mobile

Unable to set up account on my mobile

I was initial successful in setting up emails on my users mobile not until recent their password will not go in. I advised them to delete their account on their phone and try to set it up again. But now the account will not set up using exchange server and imap as well. All it give is "unable to set up account, Authentication Failed.
Please help me.
Cheers
Olu