A message from NetBeans "Browser refused to debug this tab, Close Chrome developer tools(or any other browser debugger") and try again"

[Varuna Seneviratna]

Hi,
       When an HTML5 application is run in NetBeans the message "Browser
refused to debug this tab, Close Chrome developer tools(or any other
browser debugger") and try again" is given by NetBeans, Why? no developer
tools are open, nor any other browser debugger.

Varuna