having the exact same problem and haven't figured it out yet.
i've tried factory resetting the camera, reloading the firmware, reinstalling the viewer software...getting a little frustrated with it.
the SD card works fine, i can read in on my mac..and any alarms are definitely recorded on the card...so it must be something to do with either the network speed, or admin rights to the disk...wonder has it anything to do with anti-virus..must try that next
any other ideas welcome