I was getting below javascript error everytime i run my visual studio asp.net web pages:
this._form is null or not an object
Because of this error all my AJAX controls and page postback stopped working.
As the error clearly states that it is a JavaScript error so i started checking all my Javascript code.
Finally searching on the internet i found the cause and cure of this problem.
Cause:
If you are including javascript files in the page herader like the below:
<script src="aj.js" type="text/javascript" />
Solution:
Here the closing of script tag is not correct, through its an empty tag but somehow it needs to be closed as a old fashioned way, like done below:
<script src="aj.js" type="text/javascript"></script>
Close the javascript tag properly and see the magic yourself.