Make sure that the lateral, adjustable top guides (picture) are set correctly in lateral position as well as in height. They shall guide and hold the stripes as flat as possible over both sensors B260 and B261. Both sensors need to be reached at same time, otherwise the error will occur.
If the lateral guide is too far away from the sensor, the sheet might bulge. Therefore move the lateral guide closer to the sensor.
Do not loosen the screw marked red. The standard setting for top guide should be approx. X = 72 mm.