"This operation requires IIS integrated pipeline mode."

I was having the same issue and I solved it doing the following:

1. In Visual Studio, select "Project properties".

2. Select the "Web" Tab.

3. Select "Use Local IIS Web server".

4. Check "Use IIS Express"

Your Application Pool is in classic mode but your Application need integrated mode to fire. change it to Integrated Mode:

1. Open IIS Manager

2. Application Pool

3. Select pool that your app are run in it

4. In right panel select Basic Setting

5. Manage Pipeline Mode change to Integrated

Try using Response.AddHeader instead of Response.Headers.Add()