Variable used without being declared

Include <WinAPIEx.au3>
$sProg = "downloader.Exe"
$sTitl = "0"
Run("Downloader.exe")
Do
$sTitl = _WinGetForProc ($sProg)
Until $sTitl<>"0"
Func _WinGetForProc ($sProcName)
$alist = ProcessList($sProcName)
For $i = 1 to $alist[0][0]
  $iProcPid = $alist[$i][1]
Next
$aData = _WinAPI_EnumProcessWindows($iProcPid, 1)
$iWin = $aData [1][0]
$sTitl = WinGetTitle( $iWin )
Return $sTitl
EndFunc

Do
sleep(1000)
$fVisible = ControlCommand ( $sTitl, "",'[CLASS:Button; INSTANCE:1]', "IsVisible" )
If $fVisible = "1" Then
	WinActivate($sTitl,"")
	ControlClick($sTitl, "", "Button1")
EndIf
Until $fVisible = "0"

For $i = 1 to $alist[0][0]
  $iProcPid = $alist[$i][1]
Next