a) You have not attached the pressurized filter holder to the brew unit properly.
b) The upper edge of the filter holder and/or filter holder intake are not clean.
c) There is too much ground coffee applied in the ground coffee filter.
d) The wrong filter holder has being applied (E.S.E. filter- vs pre-ground filter holder).
e) The E.S.E. adapter & E.S.E. filter holder have being applied in the wrong order. (see below picture for the right order)