Recently my college got problem in AJAX file upload control which is “AJAXControlToolKit required Ajax4.0 script”
see the error detail in below snap.
So the reason behind this he is using AJAX script manager not AJAX toolkit script manager. Now you have question when to use script manager and when to use AJAX toolkit script manager so my suggestion is always use AJAX toolkit script manager because it is faster than script manager in many ways and if you try to find difference between AJAX script Manager & AJAX Toolkit script manager then you will find AJAX toolkit script manager is best option for enhancement of your web app performance also.
(If you have not downloaded AJAX toolkit Script Manager then you can download latest AJAX toolkit and install on your machine)
So Enjoy weekend.
Happy Makar sakranti (Indian New Year)
Thanks & Best Regards,