Permission to write to EventLog from C# / VB .NET

Hello,
I have application which need to write to windows event log. I've created additional log in windows and granted full control on it to ASPNET user. The developer writing web application reported that he encoutered security problem while trying to write to event log.
So I created windows form application (One form with one button) code below and run on the server.
I got this error:
"Application attepted to perform an operation not allowed by the security policy. To grant this application the request permission, contact your system administrator, or use the Microsoft .NET Framework Configuration tool.
Request for the permission of type
'System.Diagnostics.EventLogPermission,System,Version=2.0.0.0,Culture=neutral,PublicKeyToken=b77a5c561934e089' failed."

What should I do? Please give very detailed information what and how, because I've never used .NET framework configuration.
Best Regards.
FooKyStart Free Trial

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private void button1_Click(object sender, EventArgs e)
        {
            counter++;
            label1.Text = "NO: " + counter;
            System.Diagnostics.EventLog el = new System.Diagnostics.EventLog(textBox1.Text);
            el.Source = "MyApp";
            el.WriteEntry("MyMessage",System.Diagnostics.EventLogEntryType.Information);
        }