"The command is not available" error message when you try to start the Out of Office Assistant in Outlook 2002 or 2003
Resolution:
Quit Outlook if it is running.
Press CTRL+ALT+DELETE, and then click Task Manager.
Click the Processes tab, and then verify that Outlook.exe does not appear in the list of processes.
Quit Task Manager.
Click Start, click Run, type regedit in the Open box, and then click OK.
Locate and then click the following registry key:
HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook
(10.0 for 2002, 11.0 for 2003, 12.0 for 2007)
Right-click the Resiliency subkey (if it exists), and then click Rename.
Type Resiliency.old, and then press ENTER.
Quit Registry Editor.
Start Outlook, and then click Out of Office Assistant on the Tools menu.
Source:
http://support.microsoft.com/kb/327353