For those getting the failed upgrade messages, we have also experienced isolated problems upgrading some units from v.3.3.x to v.3.4.2 on about half of our DS-76XXNI-E2 units. I recommend going to v3.4.0 or v3.4.1 first and then try upgrading to v3.4.2. If that doesn't work then try a bootloader
tftp upgrade (if you have a working firmware you may have to reboot a few times to get it to look for a tftp upgrade at boot up and make sure spanning tree is turned off on your switch or it will block the port during the bootup tftp upgrade attempt). I can also report that in situations where it required multiple steps to upgrade to v3.4.2 the only way to downgrade to an earlier than v.3.4.2 version was via tftp. Also, if downgrading from Euro/ML to a USA image I recommend downgrading all the way to v3.3.4 build 150616 to prevent configuration file corruption.
Lastly, v3.4.2 seems to work best with DS-2x22,2x42 Cameras running v5.3.8 build 151224 (not on the Euro ftp/website yet but available to distributors and shipping on all new WR Value Plus line Cameras) especially now that sensitivity and picture settings are consistent between NVR and Camera.
Hiky, we have been promised an early release firmware (v3.5.x) for the NVRs that will support Smart Event features (ie. intrusion detection and line crossing) at an NVR level. Hikvision says that are going to set it our way this month so if and when we get it I will let you know if we will finally be able to set (and retain) Smart Events on Hikvision NVRs.