Meridian 61C VERSION 2921 Release 3. After a recent upgrade everyday, at random, some of the phonesets(M3903) get hung. The display goes blank, no voice, but the phone remains alive. It's status is shown as IDLE. The menus can be accessed using the phoneset buttons. Even a call can be dialed and received, but there is no speech and no display. The problem gets resolved without any intervention after an indefinite time (usually hours). Can any one help?