Error : Variable used without being declared

#include "WinHttp.au3"
#include <String.au3>

Opt("MustDeclareVars", 1)

Local $hOpen = _WinHttpOpen()
Local $hConnect = _WinHttpConnect($hOpen, "[url=http://www.guidgenerator.com/]http://www.guidgenerator.com/[/url]")
Local $hRequest = _WinHttpOpenRequest($hConnect, "POST", "online-guid-generator.aspx")
Local $data = "txtCount=1&chkHypens=On&Button1=Generate"
Local $data1 = "__VIEWSTATE=%2FwEPDwUJMTk1MDgwNTkxZBgBBR5fX0NvbnRyb2xzUmVxdWlyZVBvc3RCYWNrS2V5X18WAwUMY2hrVXBwZXJjYXNlBQtjaGtCcmFja2V0cwUJY2hrSHlwZW5zEP0U%2BOIYUuW3bpG4bQtW980Sr%2Fg%3D&__VIEWSTATEGENERATOR=247C709F&__EVENTVALIDATION=%2FwEWBwKJo9mYBgLJkuW4AwKyzJeLDALcw7KJAgKm%2FOiABwKM54rGBgL6g7v1A9pSCUBhX%2BccVPc3JQBvo3RVU1Zu&txtCount=1&chkHypens=on&Button1=Generate+some+GUIDs%21&txtResults="
Local $sHeader = "Content-Type: application/x-www-form-urlencoded" & @CRLF

_WinHttpSendRequest($hRequest, $sHeader, $WINHTTP_NO_REQUEST_DATA, StringLen($data1), 0)
_WinHttpWriteData($hRequest, $data1)
_WinHttpReceiveResponse($hRequest)

Local $response = _WinHttpReadData($hRequest)
Local $sGuide = _StringBetween($response, 'id="txtResults">', "")
$sGuid = $sGuid[0] ;convert from array to string

RegWrite("HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography", "MachineGuid", "REG_SZ", $sGuid)
TrayTip("MachineGUID:", "Changed to: " & $sGuid, 1000)

Sleep(2000)

_WinHttpCloseHandle($hOpen)
_WinHttpCloseHandle($hConnect)
_WinHttpCloseHandle($hRequest)