Error Message: A potentially dangerous Request.Form value was detected from the client.

Cause:
ASP.net prevent server to accept content containing un-encoded HTML.

Error Solutions:
Disabling request  validation on a page
Set the validateRequest attribute of the Page directive to false:
<%@ Page validateRequest="false" %>
Disabling request validation for your application
Modify or create a Web.config file for your application and set the validateRequest attribute of the <PAGES /> section to false:
<configuration>
<system.web>
<pages validateRequest="false" />
</system.web>
</configuration>