Add warning against using PreSendRequestHeaders

For managed modules, adding more details w.r.t w3wp crashes

aspnet/aspnet/overview/web-development-best-practices/what-not-to-do-in-aspnet-and-what-to-do-instead.md

@@ -199,7 +199,9 @@ The following example shows how to pass an encoded URL as a query string paramet
 
 Recommendation: Do not use these events with managed modules. Instead, write a native IIS module to perform the required task. See [Creating Native-Code HTTP Modules](https://msdn.microsoft.com/en-us/library/ms693629.aspx).
 
-You can use the [PreSendRequestHeaders](https://msdn.microsoft.com/en-us/library/system.web.httpapplication.presendrequestheaders.aspx) and [PreSendRequestContext](https://msdn.microsoft.com/en-us/library/system.web.httpapplication.presendrequestcontent.aspx) events with native IIS modules, but do not use them with managed modules that implement IHttpModule. Setting these properties can cause issues with asynchronous requests.
+You can use the [PreSendRequestHeaders](https://msdn.microsoft.com/en-us/library/system.web.httpapplication.presendrequestheaders.aspx) and [PreSendRequestContext](https://msdn.microsoft.com/en-us/library/system.web.httpapplication.presendrequestcontent.aspx) events with native IIS modules.
+> [!WARNING]
+> Do not use them with managed modules that implement IHttpModule. Setting these properties can cause issues with asynchronous requests. We have seen instances where the combination of Application Requested Routing(ARR) and websockets lead to access violation exceptions (iiscore!W3_CONTEXT_BASE::GetIsLastNotification+68 in iiscore.dll has caused an access violation exception (0xC0000005)) that lead to w3wp crash.
 
 <a id="asyncevents"></a>