In Microsoft Outlook 2002 and 2003 when you access the out of office assistant you may get the error “The command is not available. See the program documentation about how to use this extension.” To resolve this problem requires you edit the registry.
The following key needs to be deleted HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Resiliency for Outlook 2003 or HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\Resiliency for Outlook 2002.
Use regedit or regedt32 to access the registry. Locate the key and delete it. Then restart Outlook and you’ll have access to the Out of Office Assistant.