The parameter 'from' cannot be an empty string. Parameter name: from - asp.net

Question

Ok, so basically I have a comments form on my website. People but comments in the comment box and it emails the comments to my email. The email part works fine and goes through. However, the error comes when I try to clear the form fields. It gives me an error saying:
Error: The parameter 'from' cannot be an empty string.
Parameter name: from
So anyone have any thoughts? like I said the email part works fine its just clearing the fields is giving me trouble
here is the code:
Imports System.Web.Mail
Imports System.Text
Partial Class Pages_ContactUs : Inherits System.Web.UI.Page
Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim body As String = "From: " + YourName.Text + " " + Environment.NewLine + "Email: " + YourEmail.Text + Environment.NewLine + Environment.NewLine + "Message: " + Environment.NewLine + Comments.Text
Dim MM As New System.Net.Mail.SmtpClient
MM.EnableSsl = True
MM.Host = "smtp.gmail.com"
Dim cred As New System.Net.NetworkCredential("myEmail#gmail.com", "myPassword")
MM.Credentials = cred
MM.Send(YourEmail.Text, "myEmail#gmail.com", Subject.Text, body)
ClearFields()
lblEmail.ForeColor = Drawing.Color.Green
lblEmail.Text = "Your message has been sent successfuly"
lblEmail.Visible = True
End Sub
Protected Sub ClearFields()
YourName.Text = ""
YourEmail.Text = ""
Comments.Text = ""
Subject.Text = ""
End Sub
End Class

Answer 1

You must supply it, just make it yours. Basic pattern:
Using SmtpServer As New SmtpClient()
Using mail As New System.Web.Mail.MailMessage()
Try
SmtpServer.UseDefaultCredentials = True
SmtpServer.EnableSsl = True
SmtpServer.Credentials = New Net.NetworkCredential(un, pw)
SmtpServer.Port = 25
SmtpServer.Host = "smtp.address"
mail.From = New MailAddress(sender)
mail.To.Add(some address)
mail.Subject = subject
mail.Body = body
mail.Sender = New MailAddress(sender)
SmtpServer.Send(mail)
Catch
End Try
End Using
End Using