The information on what dialogs Outlook shouldn’t show again resides under the HKCU\Software\Microsoft\Office\11.0\Outlook\Options\General\ registry key in a REG_SZ value named PONT_STRING. The text in the registry value, if present, consists of a series of numbers, each followed by a comma. Each suppressed dialog corresponds to a different number. For your dialog, it's 11. So, just delete “11,†– including the trailing comma -- from the PONT_STRING registry value.
Make a backup of the registry first, of course.
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Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers