I am trying to get a Macro to run in Outlook that inserts a salutation/greeting.

When I run it, I am getting a Microsoft Visual Basic box with error:
Run-time error '5': Invalid procedure call or argument

I then click debug and it highlights the following code on line 28:

strGreetName = Left$(Msg.SenderName, InStr(1, Msg.SenderName, " ") - 1)

I am running Win7 Pro with Outlook 2010.

Thanks in advance for any help.

Here is the complete macro:

Sub Greeting()
Dim Msg As Outlook.MailItem
Dim MsgReply As Outlook.MailItem
Dim strGreetName As String
Dim lGreetType As Long

' set reference to open/selected mail item
On Error Resume Next
Select Case TypeName(Application.ActiveWindow)
Case "Explorer"
Set Msg = ActiveExplorer.Selection.Item(1)
Case "Inspector"
Set Msg = ActiveInspector.CurrentItem
Case Else
End Select
On Error GoTo 0

If Msg Is Nothing Then GoTo ExitProc

' figure out greeting line
On Error Resume Next
lGreetType = InputBox("How to greet:" & vbCr & vbCr & "Type '1' for name, '2' for time of day")
On Error GoTo 0

If lGreetType = False Then GoTo ExitProc

If lGreetType = 1 Then
strGreetName = Left$(Msg.SenderName, InStr(1, Msg.SenderName, " ") - 1)
ElseIf lGreetType = 2 Then
Select Case Time
Case Is < 0.5
strGreetName = "Good morning"
Case 0.5 To 0.75
strGreetName = "Good afternoon"
Case Else
strGreetName = "Good evening"
End Select
Else ' something else entered??
GoTo ExitProc
End If

Set MsgReply = Msg.Reply

With MsgReply
.Subject = "RE:" & Msg.Subject
.HTMLBody = "<span style=""font-family : verdana;font-size : 10pt""><p>Hello " & strGreetName & ",</p></span>" & .HTMLBody
End With

Set Msg = Nothing
Set MsgReply = Nothing
End Sub