__doPostBack is not defined

The run time/client side error __doPostBack is undefined hassled me for a few hours. There was lots of misleading/incorrect help on the net. I inserted the following line of code in the Page_Load event of the default.aspx.cs file and everything worked fine, on my system and in production with GoDaddy.

ClientScript.GetPostBackEventReference(this, string.Empty);

If the page doesn't have a control that causes a postback, __doPostBack() won't be output as a function definition. One way to override this is to include this line in your Page_PreRender():

this.Page.ClientScript.GetPostBackEventReference(<a control>, string.Empty);

This function returns a string calling __doPostBack(); but also forces the page to output the __doPostBack() function definition.

Here's why this was happening to me: I accidentally forgot that script tags must always have closing tags:

<script src="/Scripts/appLogic/Regions.js" />

I corrected the script tag:

<script src="/Scripts/appLogic/Regions.js" type="text/javascript" ></script>

and sanity returned.