The error message “Server failed to add header after sending HTTP headers” typically occurs when you attempt to modify or add an HTTP header after the response headers have already been sent to the client. Once the response headers are sent, you cannot modify them.
To resolve this error, you can follow these steps:
- Make sure you are not modifying the response headers after you have sent the response content or started streaming the response.
- Check your code for any places where you might be modifying the response headers after the response has already been sent. This can happen if you are using asynchronous programming or if there are multiple points in your code where headers can be modified.
- If you need to modify the response headers dynamically, ensure that you do so before sending any content or starting the response stream. Headers should be set before calling the
Here’s an example to demonstrate the correct order of setting headers and sending content:
// Set the response headers
Response.ContentType = "text/plain";
// Write the response content
- If you are using any third-party libraries or frameworks that manipulate the response headers, check their documentation for any specific guidelines on when and how to modify headers.
By ensuring that you set or modify the response headers before sending the response content, you should be able to resolve the “Server failed to add header after sending HTTP headers” error in C#.