Check that the seal is correctly in place.
The watertight seal goes on TOP of the metal blade assembly, which goes into the black blade assembly holder.
Check that all 4 blades are properly positioned on the motor base.
Check that the black base is correctly screwed onto the base of the jug; tighten if necessary.
The proper blade assembly can be found on page 22 of your product manual.
Check that maximum quantities have been respected.