WinForms Global Exception Handling?

Since its a winforms app you could just enclose Application.Run(new MainForm()); in a try catch block.

static void Main()
{
try {
 Application.Run(new MainForm());
} catch(SystemException)//just as an example 
{
 //log or handle the error here. 
}
}

I don't know any implications this kind of solution would cause, but I just told you what you needed.

Other options are subscribing to Application.ThreadException event.

Read more here: unhandledexceptions

There is also AppDomain.UnhandledException and you should read the difference between them here on MSDN.

From MSDN :

For certain application models, the UnhandledException event can be preempted by other events if the unhandled exception occurs in the main application thread.

In applications that use Windows Forms, unhandled exceptions in the main application thread cause the Application.ThreadException event to be raised. If this event is handled, the default behavior is that the unhandled exception does not terminate the application, although the application is left in an unknown state. In that case, the UnhandledException event is not raised. This behavior can be changed by using the application configuration file, or by using the Application.SetUnhandledExceptionMode method to change the mode to UnhandledExceptionMode.ThrowException before the ThreadException event handler is hooked up. This applies only to the main application thread. The UnhandledException event is raised for unhandled exceptions thrown in other threads.

If #26 is an exception then you can use AppDomain.CurrentDomain.UnhandledException event. If it's just a return value, then I don't see any chance to handle that globally.

public static void Main()
{
    AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(MyHandler);

    // start main thread here
}

static void MyHandler(object sender, UnhandledExceptionEventArgs args) 
{
    Exception e = (Exception) args.ExceptionObject;
    Console.WriteLine("MyHandler caught : " + e.Message);
}

With the reference of Centralized Exception Handling in C# Windows Application, I found one of good solution :

static class Program
{
    [STAThread]
    static void Main()
    {
        // Add handler to handle the exception raised by main threads
        Application.ThreadException += 
        new System.Threading.ThreadExceptionEventHandler(Application_ThreadException);

        // Add handler to handle the exception raised by additional threads
        AppDomain.CurrentDomain.UnhandledException += 
        new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);

        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new Form1());

        // Stop the application and all the threads in suspended state.
        Environment.Exit(-1);            
    }

    static void Application_ThreadException
        (object sender, System.Threading.ThreadExceptionEventArgs e)
    {// All exceptions thrown by the main thread are handled over this method

        ShowExceptionDetails(e.Exception);
    }

    static void CurrentDomain_UnhandledException
        (object sender, UnhandledExceptionEventArgs e)
    {// All exceptions thrown by additional threads are handled in this method

        ShowExceptionDetails(e.ExceptionObject as Exception);

        // Suspend the current thread for now to stop the exception from throwing.
        Thread.CurrentThread.Suspend();
    }

    static void ShowExceptionDetails(Exception Ex)
    {
        // Do logging of exception details
        MessageBox.Show(Ex.Message, Ex.TargetSite.ToString(), 
                MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
}  

In the above class, we shall attach an event handler to two events. It is better to attach these events as soon as the main method starts.

Application.ThreadException - This event will be raised when an exception is thrown in the main thread. If we add an event handler, then the exception is handled over the method.

AppDomain.CurrentDomain.UnhandledException - This event will be raised when an exception is thrown in the additional threads used in the application. The worse scenario here is as soon as the handlers' execution gets over, the exception is again thrown whereas the application ends. This need to be handled. Here I have used a bit of code to handle this situation and continue the execution of the application without interruption.

The logic I have used to overcome this situation is just suspending the thread in the event handler, so that the application continues to work fine. Again a problem arises in suspending this thread. When the main form is closed, the application normally needs to exit, but as the thread is in suspended state, the application will still remain running. So to exit the application completely and stop the process, Environment.Exit(-1) must be called before the ending of the main method.