MkDir not working

I have the following code (that I borrowed) and was using it to export some worksheets to a new workbook. It worked fine for about 4 times, now it says it can't find the file path and stops on the "MkDir FolderName" line.

Sub ExportWorkbook()
    Dim FileExtStr As String
    Dim FileFormatNum As Long
    Dim Sourcewb As Workbook
    Dim Destwb As Workbook
    Dim sh As Worksheet
    Dim DateString As String
    Dim FolderName As String
    
For Each sh In ThisWorkbook.Worksheets
With sh
    If LCase(Right(.Name, 2)) = "sd" Then
        .Visible = xlSheetVisible
    End If
End With
Next sh
Sheets("Order").Visible = xlSheetHidden

    With Application
        .ScreenUpdating = False
        .EnableEvents = False
        .Calculation = xlCalculationManual
    End With

    'Copy every sheet from the workbook with this macro
    Set Sourcewb = ThisWorkbook

    'Create new folder to save the new files in
    DateString = Format(Now, "mm-dd-yyyy hh:mm")
    FolderName = Sourcewb.Path & "\" & Sourcewb.Name & " " & DateString
    MkDir FolderName

    'Copy every visible sheet to a new workbook
    For Each sh In Sourcewb.Worksheets

        'If the sheet is visible then copy it to a new workbook
        If sh.Visible = -1 Then
            sh.Copy
        'and so on

The sourcewb is in a folder on my desktop. When this worked correctly, it created a new folder within that same folder. (I haven't moved anything.) That would be great but I'm over my head here... Any help is greatly appreciated. Thank you!