Correct code based on your sample files:

Sub M_snb()
    sn = Filter(Split(CreateObject("wscript.shell").exec("cmd /c Dir G:\OF\table_*.csv /b /s").stdout.readall, vbCrLf), ".")
     
    With CreateObject("scripting.filesystemobject")
        For j = 0 To UBound(sn)
            sp = Split(.opentextfile(sn(j)).readall, vbLf)
             
            For jj = 0 To UBound(sp) - 1
                sp(jj) = Log(Split(sp(jj), ",")(5)) / Log(10)
                If jj = 0 Then
                  y = sp(jj)
                Else
                  y = y + 100 * (sp(jj) - sp(jj - 1)) ^ 2
                End If
            Next
            c00 = c00 & vbLf & sn(j) & "|" & y
        Next
    End With
     
    MsgBox c00
End Sub