Delegate Settings Error

I have a user that is trying to give another person delegate permissions -
"Editor" permission to her calendar. He is getting a message that states:

The Delegates setting were not saved correctly. Cannot activate
send-on-behalf-of list, You do not have sufficient permission to perform this
operation on this object.

The suggested solution on the internet seems to be:


Connect to your mail server.
Open Active Directory Users and Computers, and then click Advanced Features
if it is not already selected on the View menu.
Expand your domain, and then locate the user’s Organizational Unit (OU).
In the right pane, right-click the user who is experiencing the delegate
issue, and then click Properties.
Click the Security tab, locate the SELF account, and then click Write
Personal Information .
Make sure the Write permissions check box is selected, and then click OK.


However,

these are the only options that I see:

Delete mailbox storage
Read permissions - checked
Change permissions
Take permissions
Full mailbox access - checked
Associated external account
Special permissions


i.e can't find the WritePersonal Information option anywhere.

We are using Exchange 2003 with the latest service pack on windows 2003 sp2.
On the client desktop the user is using Outlook 2003 sp3.


Can someone please help.

Thanks