Hello I'm new on DNN

I've got a problem on custom module with web api interface. There is a "controller" class with a public method with [DnnAuthorize] annotation.

On my IIS 7.5 NET 4.0 is ALL OK (great!) ...but when I publish on Win Hosted domain works only DNN site (page navigation) and custom ASXC controls, but not WEB API functions. 

This is the error:

"This server variable cannot be modified during request execution."

[HttpException (0x80004005): This server variable cannot be modified during request execution.]

   System.Web.HttpServerVarsCollection.SetServerVariableManagedOnly(String name, String value) +2531261

   System.Web.HttpServerVarsCollection.SynchronizeServerVariable(String name, String value) +28

   System.Web.HttpRequest.SynchronizeServerVariable(String name, String value) +112

   System.Web.Hosting.IIS7WorkerRequest.GetServerVarChanges(HttpContext ctx) +308

   System.Web.Hosting.IIS7WorkerRequest.SynchronizeVariables(HttpContext context) +9697222

   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +151

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.34274

I found a MS article:

https://support.microsoft.com/en-us/kb/2605401

To stop the exception from occurring, choose one of the following options:

1) Configure the application pool to run in Classic mode instead of Integrated Pipeline mode. 

2) Use native or managed Http Modules to handle authentication notifications. 

.... What can I do?