We have a cisco 8945 IP Phone. The phone works fine in the day but when the next day the user tries to use the phone there is not response. There is a light on the the navigation centre button. But pressing the button does not get the phone out of sleep mode. According to the document the phone should get out of the sleep mode by pressing the centre button or by  picking  up the receiver. But even after doing this there is no response. Finally we have to unplug the network cable and plug it back. Only then the phone starts working fine. This we have to do it daily.

CUCM ver: 8.6.2

Regards,

Devraj