How about you try this code.
---------------------------
try
{
File.Copy(Application.StartupPath +
"\\DBName.mdb", Application.StartupPath +
"\\Backup\\" + DateTime.Now.Day.ToString() +
"_" + DateTime.Now.Month.ToString() +
"_" + DateTime.Now.Year.ToString() +
"_DBBackUp.mdb")
}
catch (Exception)
{
MessageBox.Show("Database already existde for Current Day")
}