Hi Damian,
After further debugging, I realise the problem does not occur on a live server (Hostgator). It only happen locally on my computer using XAMPP, and it only happens after I upgraded to WordPress 3.9.
I have given some description and screen shots of the error that I seen on my local computer and have emailed to support@css-javascript-toolbox.com. Hope you can take a look at the problem and point me to the correct direction to resolve it as I cannot replicate this problem on a live server for you guys to debug.
Regards
Justin