ASP.NET Request.Form Performance

I used a HttpHandler to implement a light-weight web service targeted for high performance. It requires a POST with content-type application/x-www-form-urlencoded. The web service does many tasks including decryption, database work, business logic and so on. During load testing, the performance monitor (ANTS and Visual Studio) point to a single line of code that is taking the majority of time, in fact 67%.

string value = context.Request.Form[MY_FORM_KEY];

At the bottom of the call stack for this line of code, the performance monitor, says this call:

System.Web.Hosting.UnsafeIISMethods.MgdSyncReadRequest();

is the culprit.

Can anyone help please explain?! The application is in .Net 4, published as release, IIS 7, on Windows Server 2008.

Thank you, Joey J. Barrett