I was also told to land my drone immediately. Have you experienced this error? Any solution to this error? Thanks!

Hello, I had the same problem, but I was flying in fog and ultrasonic sensor does not work in fog well

Also, there is no ultrasonic sensor in Spark :-D Obviously, DJI developers have just reused some code from Mavic and never bothered to rename this to "bottom infrared sensor" or similar.

Hi, sir. Please note that flying your spark across fog or cloud may cause malfunction of vision system and brings error message. If the message appear when you fly your spark in sunny day, please ensure that no stain on the camera. Did you crash your spark before? If you do nothing wrong, please export the flight data and the black box for further check:

Seems to be rather widespread. DJI Moderators?  This is a software problem, when a fix be available, I was fly both times in sunlight dew point 56, so it is not fog or rain.

I had the same error 2 days ago flying my spark.

Had my IMU and Compass calibrated, started flying and in less than 5 minutes I got the error.  I was flying in clear skies, no fog or clouds.

I am using the latest firmware and the latest app as well.