It means you have skills in your attack skills that doesn't belong to either. For weapons to switch there needs to be atleast one attack skill that is not the general attack added to the attack skill bar.
For example : You are a wizard/Bard. You want to cast Noise and Moving/Swing march. You add them in buff column. In the attack column you add all the wizz attack skills,that you want to use, such as fireball, icespear and so on.
Make sure you have your secondary weapon in the inventory slot designated for the weapon [So if it says slot 1 you put it in inventory Slot number 1 on page 1 etc] Always save settings.
Look in the Specific mob designation (Such as attack iteration for event mobs, pt giants etc, if you have added attack skills that does not belong there.)
Try this. If it doesn't work, visit Bot-cave.net and ask there.