We have got the same issue. this appear to be a known error by microsoft and
is detailed in KB913807. i have included the section of the article that
deals with this
Known issue in Outlook 2003 Service Pack 2
When you try to add a delegated user on the Delegates tab in the Outlook
options after you added the user and defined the folder permissions, you
receive the following error message:
The delegate settings were not saved correctly. Unable to activate
send-on-behalf-of list. You do not have sufficient permission to perform this
operation on this object.
This also occurs when you try to modify existing delegations.
For delegate access to be assigned successfully, the Write Personal
Information must be correct for the SELF account. Additionally, when the user
logs on to Exchange Server, Exchange Server must return a domain controller
(DC) and a global catalog (GC) that are local to the user account's domain so
that the publicDelegates attribute can be written.
For more information about this issue, click the following article number to
view the article in the Microsoft Knowledge Base:
813929 (
http://support.microsoft.com/kb/813929/) A user cannot set another
user as a delegate in Outlook
To work around this issue, add Write Personal Information permission to the
SELF account on the user who is trying to add the delegate. To do this,
follow these steps: 1. Open Active Directory Users and Computers, and then
click Advanced Features if it is not already selected on the View menu.
2. Expand Your_Server, and then locate the user’s Organizational Unit (OU).
3. In the right pane, right-click the user who is experiencing the delegate
issue, and then click Properties.
4. Click the Security tab, locate the SELF account, and then click Write
Personal Information .
5. Make sure the Write permissions check box is selected, and then click OK.