C#

//opens streamreader to read in readIDs
     StreamReader objReader = new StreamReader(readIDPath + "readIDs");
     POPMessageId sLine;

     int i = 0;
     //read until end of file
     while (objReader != null)
     {
           sLine = objReader.ReadLine();    // <-- GET ERROR HERE
           if (sLine != null)   
           {
               //add each line of text file in
               readIDs[i] = sLine;
               i++;
            }
      }
      objReader.Close();

I've tried casting the string to type POPMessageId but that doesn't fix it. Is there a way I can store the Id's in the file as type PopMessageId or retrieve them as this type? I'm new to working with files in C# but I'm sure it must be possible.

NetworkCredential loginInfo = new NetworkCredential(gMailAccount, password);
MailMessage msg = new MailMessage();

msg.Sender = new MailAddress(from, displayname);
msg.ReplyTo = new MailAddress(from, displayname);
msg.From = new MailAddress(from, displayname);
msg.To.Add(new MailAddress(to, "Jassim Rahma"));
msg.Subject = subject;
message = message.Replace(@"\r\n", Environment.NewLine);
msg.Body = message;
msg.Priority = MailPriority.High;
msg.IsBodyHtml = true;

Attachment mail_attachment = new Attachment(Application.StartupPath + "\\rbuilder.log");

if (technical_data == true)
{
    msg.Attachments.Add(mail_attachment);
}

SmtpClient client = new SmtpClient("smtp.gmail.com");
client.Port = 587;
client.EnableSsl = true;
client.UseDefaultCredentials = false;
client.Credentials = loginInfo;
client.Send(msg);

MessageBox.Show("Thank you." +Environment.NewLine + Environment.NewLine + "Your email was receieved.", "Feedback", MessageBoxButtons.OK, MessageBoxIcon.Information);

return true;

private void treeViewRekeningen_AfterCheck(object sender, TreeViewEventArgs e)
{
	Boolean ret = false;
	TreeNode node = e.Node;
	if (node.Nodes != null)
	{
		foreach (TreeNode subnode in node.Nodes)
		{
			subnode.Checked = node.Checked;
		}
	}

	if (e.Node.Checked == true)
	{
		ret = true;
	}
	else
	{
		doorloopTreeview(node, ref ret);
	}
	if (ret == false)
	{
		Console.WriteLine("No node is checked")
	}
	else
	{
		Console.WriteLine("At least one node is checked")
	}
}

private void doorloopTreeview(TreeNode parent, ref Boolean gevonden)
{
	if (gevonden == false)
	{
		foreach (TreeNode node in parent.Nodes)
		{
			doorloopTreeview(node, ref gevonden);
		}
		if (parent.Checked == true)
			gevonden = true;
	}
}