A firmware update was recently released for the NVR6XX-4KS2 series devices.
Information, instructions, and download links can be found Here
From Dahua Wiki
The video window of control installation displays “ ” when I log in the IPC.
- IE permission setting is not correct, add IPC IP as trusted sites.
- Set IE “Internet Option > Security > Custom Level > Active X control and plug-in” all enabled.
- You need to log in IPC as an administrator in WIN 7 system for the first time.