Depends on your version.
Read this:
http://www.outlook-tips.net/archives/2004/20041105.htm

Signature
Russ Valentine
[MVP-Outlook]
Russ,
If I create a distribution list using the address book option as follows it
gives error while adding members:
Click Address Book icon on the toolbar
Click File/New Entry
Choose Personal Distribution list and click OK.
Then when you try to add members, it gives error.
However if I click on Contacts and then File/New Distribution list, it works
fine and there is no error.
Why this difference in behavior? It appears that both methods are the same
yet one gives an error!
Why???
> Depends on your version.
> Read this:
[quoted text clipped - 5 lines]
> > to
> > add them individually?
Russ Valentine [MVP-Outlook] - 06 Feb 2007 22:30 GMT
The address book view has never been the correct interface for data entry.
The options to do so should not even exist on its menus and are simply a
sloppy holdover from a decade ago when when Outlook actually used a separate
address book. It has not done so for years. Never try to enter or edit data
in the address book view.

Signature
Russ Valentine
[MVP-Outlook]
> Russ,
>
[quoted text clipped - 28 lines]
>> > to
>> > add them individually?
mcp111 - 07 Feb 2007 00:55 GMT
Thanks.
> The address book view has never been the correct interface for data entry.
> The options to do so should not even exist on its menus and are simply a
[quoted text clipped - 33 lines]
> >> > to
> >> > add them individually?