How do I get rid of the popup - This file has been modified outside of the source editor

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C#

ASP.NET

I am reading all the data from "data.txt" and then deleting all the data from "data.txt" but I get this popup at the server:

This file has been modified outside of the source editor.  
Do you want to reload it?

How do I not receive the popup?
Here is my code:

protected void Button2_Click(object sender, EventArgs e)
        {
            string lines = File.ReadAllText(Server.MapPath("~/data.txt"));
            TextBox2.Text = lines.ToString();
            File.Delete(Server.MapPath("~/data.txt"));
        }