A potentially dangerous Request.Form

The post contains HTML elements (the <p> tag, in your case) - this can be indication of a cross site scripting attack, which is why asp.net does not allow it by default.

You should either HTML encode before submitting (best practice), or disable the warning and potentially expose yourself to XSS.

In the web.config file, within the tags, insert the httpRuntime element with the attribute requestValidationMode="2.0". Also add the validateRequest="false" attribute in the pages element.

<configuration>
  <system.web>
   <httpRuntime requestValidationMode="2.0" />
   <pages validateRequest="false" />
  </system.web>
</configuration>