To submit any HTML contents through RichTextEditor in earlier version of ASP.NET (older than ASP.NET 4.0), we used to set ValidateRequest="false"
in the Page directives of the aspx page and it used to work, however in the ASP.NET 4.0, by default request validation is true for all .aspx pages and cannot be set false from only .aspx page directives.
In ASP.NET 4.0, we need to add following tag into web.config file along with setting Page directives ValidateRequest=false
in order to submit HTML contents
<httpRuntime requestValidationMode="2.0" />
Hope you find this useful.
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