You make some changes the ASP.net controls on your form, and possible your JQuery. You run your application and you end up with "Error: Sys.ArgumentNullException: Value cannot be null."
95% of the time I have had this issue, the problem was that I removed a control, and its references in the .cs file, but forgot it in the JQuery. So in the JQuery I was doing a .hide() on the removed control which causes the cryptic error above. To debug I simply looked for each instance of $('#mycontrolxxxxxxx').hide(); and made sure that #mycontrolxxxxxxx actually still existed. Sure enough, I forgot to remove a JQuery line. Once I removed the rogue JQuery line, the issue went away.
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