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How to Resolve Error "CS0619: 'member' is obsolete: 'text'" in C#

The Compiler Error CS0619 is a strict deprecation error. The message reads: "'Member' is obsolete: 'Specific Message'".

Unlike CS0612 and CS0618 (which are warnings), CS0619 is a hard Error. It indicates that the author of the code explicitly decided that the member is removed, dangerous, or unsupported to the point that the code must not compile if it is used. You cannot ignore or suppress this error; you must remove the reference to the obsolete member.

This guide explains why this error is non-negotiable and how to handle it.

Understanding Obsolete as Error​

The [Obsolete] attribute takes an optional second boolean parameter called error.

  • [Obsolete("Message")] → Defaults to false. Generates Warning CS0618. The build succeeds.
  • [Obsolete("Message", true)] → Sets error to true. Generates Error CS0619. The build fails.

Library authors use this when an API has been physically removed (but the stub remains to tell you where to go), or when using the old method causes immediate crashes or security vulnerabilities.

Scenario: Calling a Forbidden Method​

Suppose a library has updated its security protocols and disabled the old unencrypted login method entirely.

Definition​

public class SecureService
{
    // The 'true' flag makes this a compile-time ERROR.
    [Obsolete("This method is insecure and has been removed. Use LoginSecure() instead.", true)]
    public void Login(string user, string pass)
    {
        throw new NotSupportedException();
    }

    public void LoginSecure(string user, string pass)
    {
        // ...
    }
}

Usage with Error​

public class Program
{
    static void Main()
    {
        var service = new SecureService();

        // ⛔️ Error CS0619: 'SecureService.Login(string, string)' is obsolete: 
        // 'This method is insecure and has been removed. Use LoginSecure() instead.'
        service.Login("admin", "1234");
    }
}

Solution: Update Your Code (Mandatory)​

Because this is an error, the compiler refuses to generate the output binary. Using #pragma warning disable will not work. You strictly must follow the instructions in the error message.

Solution: read the error text ("Use LoginSecure() instead") and update your call.

public class Program
{
    static void Main()
    {
        var service = new SecureService();

        // ✅ Correct: Switched to the supported method.
        service.LoginSecure("admin", "1234");
    }
}

Comparison: CS0612 vs CS0618 vs CS0619​

CodeTypeMessageCan Suppress?Meaning
CS0612WarningGenericYes"Please stop using this."
CS0618WarningCustomYes"Please stop. Here is why/how."
CS0619ErrorCustomNo"STOP. You cannot use this anymore."

Conclusion​

CS0619 is a breaking change notification.

  1. Read the Message: The text provided by the library author is your only guide.
  2. Refactor Immediately: You cannot defer this fix. The project will not build until the offending code is removed.
  3. Check Dependencies: If you updated a NuGet package and suddenly see this, look at the package's release notes for migration guides.

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