If this message (E01) appears in the display during grinding, there is probably something wrong with the grinding mechanism and you can try to clean the grinding compartment at the top with the brush.
Does the message E01 appear in the display after grinding? Then there is probably something wrong with the slider that can be seen at the bottom of the grinding compartment. This opens when the grinder is grinding and allows the ground coffee to pass through into the filter bag.
When the grinding process is complete, the slider should close again, but if it remains 'stuck' then there is probably dirt in between. You can clean this with the brush (or a damp cloth, etc.).