"A potentially dangerous Request.Form value was detected ..."

Server Error
"A potentially dangerous Request.Form value was detected from the client (txtMessage="Australia & New Z
...")

This error triggered due to appearance of "<", ">" in the input and the .NET framework is throwing up an error to help prevent some script injection attacks – Request Validation.

This feature was introduced with the .NET 1.1
It is good practice having this validation applied to all pages but in some cases I had to disable this feature.

There are 2 ways to do this

Disabling on a page
Set ValidateRequest="false"
Eg)


Disabling for you application
You can globally turn request validation off by adding in Web.config
Eg)