A potentially dangerous request.querystring value was detected from the client asp.net
Last Week, while working on an ASP.NET Web project, I got an issue. The issue was, when I am trying to pass unencoded HTML content into a querystring I got an error something like “A potentially dangerous Request. Form value was detected from the client”. After that I surf through the net and then got a solution. Here are possible solution which may help you. Put this below script in existing “page” directive in that .aspx file.
<%@ Page validateRequest="false" %>
If you are having more pages in your project means its very difficult to put this code in each page.so add this below tag in Web.Config file to access it globally
If you are using .Net 4.0 than you have to make one more change in Web.Config file. Add this tag in section.
If You are facing the same problem in ASP.NET MVC 3.
Add this below code in Application_Start() method.
Note: When disabling the request validation on the application make sure to validate the entire application
Hope this helps.