We have IPO SE R 8.1.x with IPO 500V2 as expansion system. We have connected ONE 1616 and THIRTEEN 1608. Out of these 13 Nos. of 1608, 4 Nos. of 1608 are working where as other 9 Nos. of 1608 do not work. These Non-working IP Phones display all the details. All 1608 are of the same version and firmware. Any solution..?