Program Exits sometimes when I use this code. Why?

So this is the code right here..

If(M2.equals("8")){
JOptionPane.showMessageDialog(null, Rules, "These are the rules you wanted to play with!", JOptionPane.INFORMATION_MESSAGE);
P2Menu();
}
This code is pretty much the same as this one
If (M2.equals("4")) {
JOptionPane.showMessageDialog(null, "You currently have " + MoneyCount2 + "$", Name1 + "'s Account Balance", JOptionPane.INFORMATION_MESSAGE);

P2Menu();
}
But for some reason when I use the first 1 after using the others multiple times it exits.. It happens only at that code.. and its strange because they are all the same pretty much.. Please help :)

Program Exits sometimes when I use this code. Why?