为什么会报错？以下是我的代码：

public bool SendEmail(string subject, string body, string to, string cc, string attachment, string mailServerAddress, string port,string mailAddress, string mailPassword)
{
try
{
string[] arrTo = to.Split(';');
string[] arrCc = cc.Split(';');
string[] arrAttachment = attachment.Split(';');

MailMessage msg = new MailMessage();
msg.From = new MailAddress(mailAddress);//发件人邮箱

foreach (string mail in arrTo)//收件人地址
{
if (mail.Trim().Length > 0)
{
msg.To.Add(new MailAddress(mail));
}
}
foreach (string mail in arrCc)//抄送人地址
{
if (mail.Trim().Length > 0)
{
msg.CC.Add(new MailAddress(mail));
}
}
foreach (string attach in arrAttachment)//附件
{
if (attach.Trim().Length > 0)
{
msg.Attachments.Add(new Attachment(attach));
}
}

msg.Subject = subject;//邮件标题
msg.SubjectEncoding = Encoding.UTF8; //主题编码

msg.Body = body;//邮件内容
msg.BodyEncoding = Encoding.UTF8;
//msg.IsBodyHtml = false; //设置为HTML格式
//msg.Priority = MailPriority.High; //优先级

SmtpClient client = new SmtpClient();
client.Host = mailServerAddress;
client.Port = int.Parse(port);
//client.UseDefaultCredentials = true;
client.EnableSsl = true;
client.Credentials = new NetworkCredential("524082999", mailPassword);

//client.DeliveryMethod = SmtpDeliveryMethod.Network;
//msg.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;
client.Send(msg);
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
return false;
}
return true;

}