The problem is that your program is dead to the world while it is saving the data to the database. The user's mouse click is sitting in the message queue, waiting for your UI thread to come back to life. When it does, the button is no longer disabled so the Click event fires.
You can solve it by emptying the message queue before you re-enable the button so the click is processed while the button is disabled:
private void button1_Click(object sender, EventArgs e) {
button1.Enabled = false;
// Save data to database
//...
System.Threading.Thread.Sleep(2000);
Application.DoEvents(); // Empty the message queue
if (!button1.IsDisposed) button1.Enabled = true;
}
Do not skip the IsDisposed test, DoEvents is dangerous because it isn't selective about what events get processed. It will happily let the user close the main window while your code is still running.
But the better solution is to not let your UI thread go dead like this. Use a BackgroundWorker to perform the save on a worker thread. This will also avoid the ugly "Not Responding" ghost window that Windows puts up when your save takes more than a couple of seconds. It probably doesn't do this yet right now, but it will a year from now when the dbase has grown. You can re-enable the button in the BGW's RunWorkerCompleted event handler.
