I Like to send email by STMPclient

I did Coding

pb_email Button clicked event

Integer li_rc
SMTPClient lnv_SmtpClient

lnv_SmtpClient = CREATE SMTPClient

//set the email account information
lnv_SmtpClient.Host = "smtp.cafe24.com"
lnv_SmtpClient.Port = 587
lnv_SmtpClient.Username = "nexterp@nextdata.cafe24.com"
lnv_SmtpClient.password = "next2724!!"
lnv_SmtpClient.EnableTLS = False
lnv_SmtpClient.Timeout = 3

//set the email message
lnv_SmtpClient.Message.SetSender("nexterp@nextdata.cafe24.com","박근열")
lnv_SmtpClient.Message.AddRecipient("h8534054@daum.net")
li_rc = lnv_SmtpClient.Message.AddAttachment("E:\파워빌더자료\디비용량줄이기.txt")
lnv_SmtpClient.Message.Subject = "SMTPClient Test Message test4"
lnv_SmtpClient.Message.TextBody = "SMTPClient example message body4"

//send the email message
li_rc = lnv_SmtpClient.Send()
IF li_rc = 1 THEN
Messagebox('SMTPClient','Mail sent successfully')
ELSE
Messagebox('SMTPClient' ,'Email sending failed. Return ' + String(li_rc) + '.', StopSign!)
END IF

DESTROY lnv_SmtpClient

// I did success to send email

But appear This MessageBox

I try click cancel button 20Times

This messageBox disappear

and then system down

How Can I Do?