Compile Error Argument not optional

Hello I am running a Macro to execute a predetermined email with a file attachment when the the excel file opens. I have this automated to open with the task scheduler. I'm a novice at best with this and have run into a issue after adding the Private Sub Workbook_Open() from my understanding this will allow the macro to run when the file opens? When I try and run this through testing I keep getting the error

Argument not Optional.... Its pointing to the line Private Sub Workbook_Open()

I have in "ThisWorkbook" in the project explorer

Private Sub Workbook_Open()

SendMail

End Sub

In the Module I have:

Sub SendMail()

Dim outApp As Object
Dim i As Long

'Check if Outlook is open
On Error Resume Next
Set outApp = GetObject(, "Outlook.Application")
On Error GoTo 0

If outApp Is Nothing Then
MsgBox "Outlook is not open. Open Outlook and try again.", vbExclamation
Exit Sub
End If

'Clear the ticks from column A
Columns("A:A").ClearContents

'The row in which the list of e-mails start
i = 6

While Cells(i, 2).Value <> ""
updateMail Cells(i, 2), Cells(i, 3), Cells(i, 4), Cells(i, 5), _
Cells(i, 6), Cells(i, 7), Cells(i, 8), Cells(i, 9), i
i = i + 1
Wend

Set outApp = Nothing

End Sub

Sub updateMail(ToBox As String, CcBox As String, BccBox As String, _
Subject As String, Message As String, AttachmentList As String, _
AttachmentSeparator As String, Action As String, row As Long)

Dim outApp As Object
Dim outMailItem As Object
Dim i As Integer
Dim attachmentArray() As String

Set outApp = GetObject(, "Outlook.Application")
Set outMailItem = outApp.CreateItem(0)
attachmentArray() = Split(AttachmentList, AttachmentSeparator)

On Error GoTo ErrorFound

'The To, CC and BCC values can send e-mails to multiple recpients
'just ensure the e-mail addresses are separated with a semicolon (
With outMailItem
.To = ToBox
.CC = CcBox
.BCC = BccBox
.Subject = Subject
.Body = Message

For i = LBound(attachmentArray) To UBound(attachmentArray)
.Attachments.Add Trim(attachmentArray(i))
Next

Select Case Action

Case "Display"
.Display
Case "Save"
.Close False
Case "Send"
.Send

End Select

End With


'Display tick or cross
ErrorFound:
If Err.Number = 0 Then
Cells(row, 1) = "ü"
Else
Cells(row, 1) = "û"
End If

CleanUp:
Set outMailItem = Nothing
Set outApp = Nothing

End Sub

Please help

If you step through the code line by line using F8, which line does the error show up on?

BSB

Sorry about that next time I will use the right tags.

When I press F8 it hight lights the SendMail in blue and Private Sub Wookbook_open in yellow.

I changed send mail to Module1.SendMail and now the error is "Variable not defined"

If it helps the object name in the modules folder is "modEmailTemplate" That is where the macro is

I changed the code to say

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The error I now get is " Expected variable or procedure, not module

That worked thank you!