I've got a US version Hikvision DS-2CD2032-I (it has a US UL sticker on it and no CH in the serial). It's currently on firmware version 5.1.6 build 140612. When I try to upgrade to 5.2 it says upgrading failed. I've updated the firmware once, I don't remember where I got the firmware from. Any idea why I can't upgrade it to any version? Thanks!