A potentially dangerous Request.QueryString value was detected from the client

Problem

The following “yellow screen” error occurs in your application:

A potentially dangerous Request.QueryString value was detected from the client ...

Description: Request Validation has detected a potentially dangerous client input value, and processing of the request has been aborted. This value may indicate an attempt to compromise the security of your application, such as a cross-site scripting attack. You can disable request validation by setting validateRequest=false in the Page directive or in the configuration section. However, it is strongly recommended that your application explicitly check all inputs in this case.

Exception Details: System.Web.HttpRequestValidationException: A potentially dangerous Request.QueryString value was detected from the client ...

Solution

See A potentially dangerous Request.Form value was detected from the client  for details.