When playing a video clip from the Netvue app Notifications screen, I received the message:
"Can’t find the video file ". Notifications continued to be received and added to the list just fine, and the camera live view was working fine. What corrected this problem for me was to go into the Android > Settings > Apps menu, and Force Stop the Netvue app. Then Storage > Clear Cache. Then disconnect the Android device from and reconnect to the WiFi network. Then restart the Netvue app. It was not necessary to do anything to the camera itself.
This occurred on a Birdfy with a 16GB SD card installed, and it had been operating correctly for two days until this problem.