You've defined 2 global variables in GUI:
public JComboBox comboBox;
public JComboBox comboBox_1;
These are un-initialized, thus null.
In the constructor, you create 2 new local variables with the same names, but you do not refer the global variables to them.
JComboBox comboBox = new JComboBox();
JComboBox comboBox_1 = new JComboBox();
As a result of this, you're getting NPE's thrown in onStart, as you're accessing the uninitialized global variables. onStart however is catching these exceptions for you, so they are never visible to you (other than the message "Error in onStart")
Solution:
In the constructor; initialize the global variables rather than creating new local ones.