T26P EHS36 Plantronics Savi W710

[duncan]

I bought a EHS36 so that I could use my Plantronics Savi W710 wireless headset with my T26P. It all works except the wireless headset mic i.e. I can hear the caller but they cannot hear me speaking. Have looked on the Forum and seen suggestions for updating the firmware on the EHS36. I have a copy of the guide for upgrading the EHS36 however, when I follow this and get to the point where it says "The phone LCD screen will prompt “Please insert expansion!” - it does not; instead I get 'Network IP Mode: IPv4'.
My T26P:
Firmware is 6.72.23.1
Hardware 4.0.1.44
Would some one be kind enough to help me resolve this problem.
Thanks