JavaScript runtime error – Sys WebForms.PageRequestManagerServerErrorException Value cannot be null.

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The error is thrown when testing a Web Application in browser, run from Visual Studio 2013+.

0x800a139e - JavaScript runtime error: Sys.WebForms.PageRequestManagerServerErrorException: Value cannot be null.  

Such error can occur if the Web application is Ajaxified.

BrowserLink is introduced in Visual Studio 2013. It can intersect AJAX calls, resulting in a JavaScript runtime error.

To test the application you can switch off BrowserLink from Visual Studio settings.

Using Browser Link in Visual Studio 2013 (source

Read more here: Source link