A client received "A potentially dangerous Request.QueryString value was detected from the client" when redirecting or posting back a form value that contains angled brackets (< >) or other suspicious characters, particularly seen in XML or HTML data.

This is a standard security feature that is enabled in ASP.NET option to check for any suspicious text that is sent to the server. This setting, when enabled, affects any module or URL/form data, not just the Storefront module. You can simply disable it in the Web.config file by setting or adding the validateRequest value to "false":

<system.web>
<pages validateRequest="false" />
</system.web>

Furthermore, you may need to set requestValidationMode="2.0" if you're running .NET 4.0. This is a known issue affecting DNN on .NET 4.0 and is not an isolated case.

<httpRuntime requestValidationMode="2.0" />