What possible contradictions or confusions do you find in the apparitions, their speeches, and their effects on Macbeth ?

One of the central contradictions the apparitions tell
Macbeth in Shakespeare's Macbeth deals with
Macduff. 

On the one hand, an apparition tells Macbeth to
"Beware Macduff."  On the other hand, Macbeth is told that he cannot be harmed by anyone
born of woman, and that he cannot be vanquished until Birnam Wood comes against his
castle at Dunsinane.  These are definitely contradictions and mixed
messages. 

This highlights the fact that Macbeth has a
choice in his fate--at least that's one way of interpreting it.  Macbeth chooses to
believe what he wants to believe.  Even though he decides to act against Macduff, he
chooses to put his confidence in the witches and believe in his
invincibility. 

Also, Macbeth is told only to beware
Macduff, not to order the slaughter of his family.  This almost certainly contributes to
desertion on the part of Macbeth's thanes and soldiers, as well as to his wife's mental
illness.  Once again (as he does in Act I when the witches tell him only that he will be
king, not that he will be king immediately by assassinating Duncan), Macbeth chooses
to apply heinous action to a rather generic statement or statements. 
 

The witches, therefore, "play" Macbeth.  They fool him
into over confidence while at the same time steering him into a terrible act that brings
about still more destruction to the kingdom of Scotland.