Passive Insufficiency - Occurs with 2 joint muscles and refers to the fact that these muscles cannot stretch maximally across both joints at the same time!
Example: Hamstrings may limit hip flexion when the knee is in full extension since they are maximally stretched in this position.
However... If the knee is flexed passively then the hip will be able to flex further - because the stretch on the hamstrings has been slackened.
Active Insufficiency - 2 joint muscles cannot contract maximally across both joints at the same time!
Example: Make a fist (finger flexors) you can make a strong fist when your wrist is in a neutral of slightly extended position. But when you flex your wrist with a clenched fist you loose some of the grip. This is because the finger flexors are unable to shorten any more than they have and so begin to extend and lose grip strength.