Hide alert error warning message box?

Gantt
#1

Hi,
How do I hide alert error warning message box?
Thanks

#2

I have several functions as per your included sample. I have tried deleting every functions e.g. zoom to fit, tooltip, dynamic scale, colors, custom lightbox, etc with no luck. This alert occurs when I delete a task.
The alert is :
Task not found id=[object Object]

So the question is: how do I hide this alert?
Thanks

#3

I have figured out the problem. Chrome console give message that the keyboard_navigation.js is the problem. This is happen after I delete task. Actually I just need the Undo feature using Ctrl-Z, so after deleting the keyboard.js, I just use the Undo button.