C# form adding to lists

C# form adding to lists

if any one is able to help thanks, it will only run after it crashes and
im not sure how to fix it thanks
{
//DOES NOT WORK YET
foreach (Client c in records)
if (nameBox.Text != c.Name)
{
records.Add(c);
}
else
{
MessageBox.Show("Member Already Exists");
}
}