Cannot programatically checkin Excel workbook to Powerpoint

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MS-Excel

PowerPoint

I have a problem that I have been working on for several weeks, exhausting all resources I have available.

I have a macro in the workbook that I am working in. The macro checks out a different spreadsheet (that I will want to make changes to) and then should check it back in. When I run the macro, it checks out the file and opens it. It then proceeds to the checkin subroutine, but fails with the message run-time error 1004 "Method 'CheckIn' of object '_Workbook' failed. I tried fully qualifying the checkin, but have the same results. I am including the code from the macro below.
Any assistance would be greatly appreciated, as I am totally stumped!
Mike

Option Base 1
Public wb0 As Workbook
Public xlFile0 As String
Public FileName0 As String
Sub Automation_Vetting_Process()
 xlFile0 = "http:// ..." 'Actual SharePoint URL
 CheckoutFile (xlFile0)
 FileName0 = wb0.Name
 CheckinFile (FileName0)
End Sub
Sub CheckoutFile(FileName As String)
' Determine if workbook can be checked out
 If Application.Workbooks.CanCheckOut(xlFile0) Then
  Application.Workbooks.CheckOut xlFile0
  Set wb0 = Application.Workbooks.Open(xlFile0)
  MsgBox wb0.Name & " is checked out to you."
 Else
  MsgBox "You are unable to checkout the at this time."
 End If
End Sub
Sub CheckinFile(FileName As String)
' Determine if workbook can be checked in
 If Application.Workbooks(FileName).CanCheckIn = True Then
  Application.Workbooks(FileName).CheckIn SaveChanges:=True, Comments:="", MakePublic:=False
  MsgBox FileName & " was checked in."
 Else
  MsgBox "You are unable to checkin the " & FileName & " spreadsheet at this time."
 End If
End Sub