Hi,
What do you mean by msgbox control?. There is no msgbox control in asp.net. There is a MessageBox class available in C# which displays a message box that can only be used with Windows Forms applications. It cannot be used with web application.
Please provide more details.
Also if the redirected page reads the content of the text file which is created by the C# exe, you should redirect to that page only after the text file is created by the exe ie., after the execution of the exe is completed. For this, you can use System.Diagnostics.Process class to run the c# exe and redirect to the aspx page in the Process.Exited event which occurs when a process exited/completed.