A site I developed was getting the error: "A potentially dangerous Request.Path value was detected from the client (&)."
This was due to how Google was indexing the pages on the site. The site is using Friendly URLs (meaning no ?Param= or &Parm=). Then Google appended the following parameters (and other values) to the end of the URL: &ct=ga&cd=.
Since there was no ?Param= .NET saw the &ct=ga&cd= as a hack. This lead me down the path of trapping that error in the Global.asax Application_Error handled. When the "A potentially dangerous Request.Path value was detected from the client (&)." error was thrown I wanted to redirect to the default home page.
The problem was the redirect did not work and the site kept going back to the custom error message page. I then found by setting Server.ClearError() I could redirect to the home page.
void Application_Error(object sender, EventArgs e)
//... other code here....
var Message = ex.Message.ToLower();
var RootURL = Common.GetAppPathMasterPages() + "default.aspx";
if (Message.Contains("does not exist") || Message.Contains("potentially dangerous request"))