Please post the full error message from the logs.
Compare your code to the "minimal example". Also make sure to add an ACToolBarLight with the designer.
Here is the full log
Registo conectado a: HUAWEI DRA-LX3
--------- beginning of crash
--------- beginning of main
*** Service (starter) Create ***
** Service (starter) Start **
** Activity (main) Create, isFirst = true **
25
%
A
Santa Clara Catholic College,asuncion
** Activity (main) Resume **
** Activity (main) Pause, UserClosed = true **
** Activity (menu_principal) Create, isFirst = true **
Error occurred on line: 0 (menu_principal)
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
at de.amberhome.objects.appcompat.ACActionBar.setShowUpIndicator(ACActionBar.java:116)
at com.anzoategui.enviapycliente.menu_principal._activity_create(menu_principal.java:384)
at java.lang.reflect.Method.invoke(Native Method)
at anywheresoftware.b4a.shell.Shell.runMethod(Shell.java:738)
at anywheresoftware.b4a.shell.Shell.raiseEventImpl(Shell.java:360)
at anywheresoftware.b4a.shell.Shell.raiseEvent(Shell.java:260)
at java.lang.reflect.Method.invoke(Native Method)
at anywheresoftware.b4a.ShellBA.raiseEvent2(ShellBA.java:144)
at com.anzoategui.enviapycliente.menu_principal.afterFirstLayout(menu_principal.java:104)
at com.anzoategui.enviapycliente.menu_principal.access$000(menu_principal.java:17)
at com.anzoategui.enviapycliente.menu_principal$WaitForLayout.run(menu_principal.java:82)
at android.os.Handler.handleCallback(Handler.java:795)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:6861)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:450)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:936)
** Activity (menu_principal) Resume **