I had the same problem but finally found a solution hidden in the depths of Logitech. It's quoted below. I had to do it a couple of times before it worked, and it seems that you need to reconnect the mouse at the same time. I didn't the first time and then the keyboard refused to work. (Finger trouble?) :-(
The following is from :-
http://logitech-en-ap.custhelp.com/cgi-bin/logitech_en_ap.cfg/php/enduser/std_adp.php?p_faqid=28&p_created=1083786523&p_sid=hwmEUpij&p_accessibility=0&p_redirect=&p_lva=&p_sp=cF9zcmNoPTEmcF9zb3J0X2J5PSZwX2dyaWRzb3J0PSZwX3Jvd19jbnQ9MTkwLDE5MCZwX3Byb2RzPTg0NCZwX2NhdHM9JnBfcHY9MS44NDQmcF9jdj0mcF9wYWdlPTEmcF9zZWFyY2hfdGV4dD1teCBkdW8gaXRvdWNo&p_li=&p_topview=1This article applies to the following products:
Cordless Access Duo
Cordless Acess Duo
Cordless access keyboard
Cordless Elite Duo
Cordless MX Duo
Cordless Navigator Duo
You may be able to reset the keyboard and resolve the problem by
clearing the keyboard capacitors. To do this, remove the batteries
from the keyboard and type continuously on as many keys as possible for
one to two minutes. This action should simulate touch-typing; you
should not press and hold only some keys down.
After you clear the capacitors, replace the batteries and synchronize the keyboard using the following procedure:
- Make sure the batteries are in correctly. A diagram on the device
itself or in the Getting Started Guide should tell you the correct
polarity for the batteries.
- Press the connect button on the receiver.
- Press the connect button on the bottom or right hand edge of the keyboard.
NOTE: If you are using a Cordless Desktop System, you must do this procedure for both the mouse and the keyboard.
The "Connect" button on the mouse is quite small and usually
requires a pencil tip or other small object to push it. Remember, ALL
Logitech cordless devices will have a synchronization button. If you
have the "Cordless Mouse" with Model Number (M/N) M-RN67, the button
will be located in a small hole on the lower portion of the back of the
mouse. You will need a paper clip to access the button.