It look like the script shouldn't run at all.
you have Dim oExcel As New Microsoft.Office.Interop.Excel.Application = Nothing
then later down you have:
wb = oExcel.Workbooks.Open(Filename:="C:\DSM Excel Files\Healthcare Logictics\Download\*.xls")
The oExcel object is set to nothing so you can't call any functions on it. You would have to create a New one.
A spelling mistake in your folder name (Logictics)
This line: xFile = xPath + "*.*.xls" will set xFile to C:\DSM Excel Files\Healthcare Logictics\Download\*.*.xls (two asterisks) is that what you want?
I don't think Excel allows you to specify wildcards on the filename of the open command. I think you would have to go through all the files in the folder one by one, the same with the Save command.
One of the easiest ways to write VBA code is to record a Macro of your actions then take that code out and amend it.