There is nothing contentious about the macro. It should not cause errors if entered as shown. The only line that needs to be changed is
.To = "someone@somewhere.com", where you need to replace the address with an actual address (though this dummy address should not cause an error).
Select a message and use the following macro to test the code and highlight where the error occurs.
Sub Test()
Dim olMsg As MailItem
On Error Resume Next
Set olMsg = ActiveExplorer.Selection.Item(1)
SendOnMessage olMsg
lbl_Exit:
Set olMsg = Nothing
Exit Sub
End Sub