I am currently a beginner in SNAP, please help me. I use SNAP for preprocessing. I don’t know which step went wrong. I tried it several times and showed this result. 
The initial data is normal, after downloading the orbit file, it is not normal. At first I thought it was the wrong download of the orbit file, but the same problem still occurred when I dealt with other steps first.
which steps have you applied and in which order?
After which step does this error occur?
The steps I applied are: apply orbit file, calibrate, deburst, multilooking, speckle filtering, terrain correction. This error occurred after applying orbit file. Then I tried to put the calibrate in the first step, and it still happened.
Is it an option to use GRD products instead. As you want to retrieve Sigma0, this should be completely sufficient and also saves you a lot of computing.