Outlook 2K – Read Receipts

I need to disable the sending of Read Receipts from a clinet computer (Win2K-Outlook2K connecting to A.D. and Exchange2K). When I open the Tools-Option-Email Options-Tracking Options diaglog box, the option to Send / Deny send receipts is greyed out (with “Send” selected). How do I activate those options so I can select DO NOT SEND read receipts?