VBA code has Runtime Error with XLSM documents but not XLS - vba

Question

This VBA code is working for me in copying and moving XLS files but when I try to run it on an XLSM file it is telling me runtime error and is highlighting;
"CurrentWB.Sheets(SheetNumber).Select 'Selects All Worksheets in Workbook"
Run-Time Error 1004: Select Method of Worksheet Class Failed
Does anyone know what the issue might be?
Sub AutoUpdate()
On Error Resume Next
Application.DisplayAlerts = False
Application.ScreenUpdating = False
Application.PrintCommunication = False
Dim SystemPath As String
Dim FilePath As String
Dim FileName As String
Dim UtilityType As String
Dim ThisName As String
Dim FlattenedFilePath As String
Dim FlattenedFileFolder As String
Dim CurrentWB As Workbook 'Workbook Stores Workbook
SystemPath = Range("Sys.Path")
UtilityType = Range("Utility.Type")
FlattenedFileFolder = Range("Flattened.Files")
FilePath = SystemPath & UtilityType
FileName = Dir(FilePath & "\*.xls")
FlattenedFilePath = FilePath & "\" & FlattenedFileFolder
Do While FileName <> ""
Set CurrentWB = Workbooks.Open(FileName:=FilePath & "\" & FileName, UpdateLinks:=3) 'Sets CurrentWB = to that long name. This becomes the name of the workbook.
CurrentWB.RunAutoMacros Which:=xlAutoOpen 'Enables Macros in Workbook
CurrentWB.Save
ThisName = CurrentWB.Name
For SheetNumber = 1 To CurrentWB.Sheets.Count 'Counts Worksheets in Workbook
If (CurrentWB.Sheets(SheetNumber).Name <> "What If") Then
CurrentWB.Sheets(SheetNumber).Unprotect ("UMC626") 'Unprotects Workbook
With CurrentWB.Sheets(SheetNumber).UsedRange
.Value = .Value
End With
CurrentWB.Sheets(SheetNumber).Protect Password:="UMC626", DrawingObjects:=True, Contents:=True, Scenarios:=True 'Protects Workbook
End If
Next SheetNumber 'Runs Through Iteration
CurrentWB.Cells(1, 1).Select 'Saves each workbook at the top of the page
CurrentWB.SaveAs FileName:=FlattenedFilePath & "\" & ThisName
CurrentWB.Close 'Closes Workbook
FileName = Dir
Loop
End Sub