Hi,
Are there more warnings in the terminal?
You can click on Create Calibration button in Preferences->Source to make sure the resulting calibration file is compatible. Here is the one generated:
%YAML:1.0
---
camera_name: calib
image_width: 848
image_height: 480
camera_matrix:
rows: 3
cols: 3
data: [ 6.0717510900000002e+02, 0., 4.3065341100000001e+02, 0.,
6.0581658900000002e+02, 2.4014419500000000e+02, 0., 0., 1. ]
Comparing both, it seems your K matrix is wrong. Make sure also that "Calibration file path (*.yaml)" is set.
cheers,
Mathieu