AddFromOutlook isn't available now

[CarlRostron]

Private Sub Command363_Click()
  DoCmd.RunCommand acCmdAddFromOutlook
End Sub

I have the above code attached to a button and I am receiving an error 'The Command or Action isn't available right now'

This is the same code from a template (and it works on there) so I clearly have done something to it in my own DB which has stopped it working. I am not sure what this could be. Maybe one of you guys can help to identify please and I can try to fix it?

I can attach files / forms where necessary.

Thanks