well, this is because your Page ValidationRequest is “True”, by default. you need to modify this in your web.config or on the page directive. You may have to set this like ValidationRequest=”False”
or in web.config under <system.web>
If you’re using .Net 3.5 or .Net 4.0 you will have to modify web.config with the following or add requestValidationMode=”2.0″ in httphandlers section.
<httpRuntime requestValidationMode=”2.0″ />
Hope this will help you to solve the issue.. please feel free to comment if you have any issues…