cmd.Parameters.Add("@eMail", SqlDbType.NVarChar(256)).Value = EmailID.Text;

Try this:

cmd.Parameters.Add("@eMail", SqlDbType.NVarChar, 256).Value = EmailID.Text;

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If you feel setting the value on the returned SqlParameter object is inefficient (I don't think it is) then you could set the value as well in 1 call, but you would need to create the SqlParameter yourself which means you need to provide all arguments (untested):

cmd.Parameters.Add(new SqlParameter("@eMail", SqlDbType.NVarChar, 256, ParameterDirection.Input, true, 0, 0, "", DataRowVersion.Current, EmailID.Text));

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Thanks.
Is there also a way to not declare the size of the field?   like -1 or something like that?

Well the size is optional in this construction so you can leave it out.

cmd.Parameters.Add("@eMail", SqlDbType.NVarChar).Value = EmailID.Text;

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cmd.Parameters.Add("@eMail", SqlDbType.NVarChar).Value = EmailID.Text;

This is what I did but do not understand why it keep truncating the stored value at 20 characters?

xxxxxxxxxxxxxxxxxxxx

12345678901234567890

I just tested it with a longer value and it was inserted in the database without a problem, can you share some more code?

            try {
                using (SqlConnection conn = new SqlConnection(@"Server=.\sqlexpress;Database=eeQ_28347912;uid=ee;pwd=ee;")) {
                    conn.Open();
                    using (SqlCommand cmd = new SqlCommand()) {
                        cmd.Connection = conn;
                        cmd.CommandText = "INSERT INTO eMailTest VALUES (@eMail)";
                        cmd.Parameters.Add("@eMail", SqlDbType.NVarChar).Value = EmailID.Text;
                        cmd.ExecuteNonQuery();
                    }
                }
            }
            catch (Exception ex) {
                MessageBox.Show(ex.Message);
            }

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CREATE PROCEDURE [dbo].[pAddUser](
      @UserName VARCHAR(20),
      @eMail VARCHAR(20),
      @Algorithm VARCHAR(16),
      @Pass VARCHAR(16)
)

The problem was the stored procedure.  Is there a way not to constraint it?

@eMail NVARCHAR,  ?

Extremely good help.  Thanks a lot.