Outlook 2003

Hi all,

We have exchange server 2003 and all users use outlook 2003.

When ever a user send an invitation on calendar to 2 directors, an message bounced back from system administrator :
“name of ex-secretary on 25/06/2008 11:18
The e-mail account does not exist at the organization this message was sent to. Check the e-mail address, or contact the recipient directly to find out the correct address”

But the ex-secretary left 3 years ago and her details has been removed since she left.
She was the secretary of those 2 directors and they shared their calendar with her.

I have look around but could NOT find where the problem is.

Has anyone come across this problem and solution, please help if you do.

Thank you for any help.