solution to Type 'System.Web.UI.WebControls.*' does not have a public property named 'ViewStateMode'.

according to this page, if you get the error,

Type 'System.Web.UI.WebControls.*' does not have a public property named 'ViewStateMode'.

all you have to do is

make sure the target framework is .net framework 4

1. change your web.config

<system.web>

    <compilation debug="true" targetFramework="4.0">

2. change the build options in the property pages for the website in visual studio.