UC520 Connection Lost

[rodinardavani]

   Hi, I have 2 questions, so first thing is that I have lost the voice VLan on the UC520 and when I try to create/modify the VLan, the UC520 becomes unreachable, and I have to hard re-start it (unplugging it and plugging it back). (Please refer to screenshots)

2. I would like to reset the UC520 to factory defaults, but any way that I try, I cannot reset it because the device will become unreachable again. (please also refer to screenshots)

Please note that I am not a pro in networking, so please kindly let me have clear and basic answers