Yea, you need a close bracket. Make the code this:

on *:TEXT:\8ball*:#:{
  /set %8ball $rand(1,12) 
  if (%8ball == 1) .msg $chan 4,1No! 
  if (%8ball == 2) .msg $chan 12,1Yes 
  if (%8ball == 3) .msg $chan 8,1Maybe 
  if (%8ball == 4) .msg $chan 9,1of course 
  if (%8ball == 5) .msg $chan 11,1Are you crazy?!?! 
  if (%8ball == 6) .msg $chan 7,1How should I know?
  if (%8ball == 7) .msg $chan 8,1HELL NO!
  if (%8ball == 8) .msg $chan 10,1As far as you know yea!
  if (%8ball == 9) .msg $chan 5,1Why should i tell you!
  if (%8ball == 10) .msg $chan 6,1If i say yes will you shut up?
  if (%8ball == 11) .msg $chan 11,1Yes that will be $20
  if (%8ball == 12) .msg $chan 3,1Ummmm...... No 
}