Try this one to see if that works.
#include<file.au3>
$filefolder = 'd:temp'
$fileextension = '*.eml'
Global $Label = 0, $lastlabel = ""
$Gui = GUICreate("Web-DMZ Count", 200, 50)
GUISetBkColor(0xFFFF00)
GUISetState()
$Label = GUICtrlCreateLabel("Jobs: 0", 20, 20)
While 1
$FileList = _FileListToArray($filefolder, $fileextension);only list files with given extension
If $FileList <> 0 Then
If $FileList[0] <> $lastlabel Then
GUICtrlSetData($Label, "Jobs: " & $FileList[0])
$lastlabel = $FileList[0]
EndIf
Else
If $lastlabel <> 0 Then
GUICtrlSetData($Label, "Jobs: Null ")
$lastlabel = 0
EndIf
EndIf
WEnd
EDIT: Fixed some code logic