[T-Mobile LG G2x] adamsk:
I have the exact same problem. I downloaded and installed the T-Mobile 2.3.3 stock ROM. I tried to follow the following guide to flash with file: V21E_00.kdz:

http://xdaforums.com/showthread.php?t=1287236

However I keep getting stuck at 4% saying there is a communication error. I have tried to go into download mode / SW upgrade mode but Windows 7 does not detect the phone. I keep getting this error:

14:47:41 : [C:\LGMobileUpgrade] Try to delete folder
14:47:41 : RemoveDirectory1 Error(2):C:\LGMobileUpgrade
14:47:41 : Start Date : 2012-10-12 14:47:41
14:47:41 : ---------- QM Testmode ---------
14:47:41 : ***** Check Tool Version *****
14:47:41 : Tool version : 1.5.4.8
14:47:41 : UpgradeDLL version : 1.2.6.7
14:47:41 : Current Dir : C:\ProgramData\LGMOBILEAX\B2C_Client
14:47:41 : LGE USB Driver Version :
14:47:41 : Android PDLV Version :
14:47:41 : Android NDLV Version :
14:47:41 : ******************************************
14:47:41 : [C:\ProgramData\LGMOBILEAX\Phone] Try to delete folder
14:47:41 : SetEmerModeAT()
14:47:41 : _IsConnectedPhone Call
14:47:57 : _IsConnectedPhone(1)
14:47:57 : 0 - NotConnected.
14:47:57 : 1 - Normal connect success
14:47:57 : 2 - Emergency connect success
14:48:08 : _IsConnectedPhone Call for SmartPhone
14:48:11 : _IsConnectedPhone(0)
14:48:11 : 0 - NotConnected.
14:48:11 : 1 - Normal connect success
14:48:11 : 2 - Emergency connect success
14:48:11 : *****CheckOS Start********
14:48:11 : Microsoft_Windows7_Professional_Service Pack 1
14:48:11 : *****CheckPCSyncPrograms Start*****
14:48:11 : PCSyncPrograms Not Found - OK and ready to upgrade
14:48:11 : Checking the connection with the cell phone...
14:48:11 : dwWaitResetTime(40000 ms)
14:48:12 : _IsConnectedPhone Call
14:48:28 : _IsConnectedPhone(1)
14:48:28 : 0 - NotConnected.
14:48:28 : 1 - Normal connect success
14:48:28 : 2 - Emergency connect success
14:48:28 : Phone Mode(1)
14:48:28 : *****GetPhoneType Start*****
14:48:42 : [011,700,147,062,092]Updating is not possible any longer due to a fatal error.\n\n[009,400,102,102,102]Disconnect from and connect the cable into your phone again and remove \nand install the battery and press the [009,700,102,102,102]'Restart'[009,400,102,102,102] button. This will resume the \nupgrade.\n\n\n\n\n\n\n\n\n\n\n\n\nPress the [009,700,102,102,102]Quit[009,400,102,102,102] button to stop the update. (_CheckPhoneType() Error)
14:48:42 : !pUpgrade->StartProcessing ... PostMsg STEP_TYPE_ENV_ERROR
14:48:42 : Page_Error ºÎºÐÀÔ´Ï´Ù
14:48:42 : ¿©±â´Â Retry ºÎºÐÀÔ´Ï´Ù
14:48:42 : OnStepMsg STEP_TYPE_ENV_ERROR delete m_pLGCyonUpdate
14:49:07 : [C:\LGMobileUpgrade] Try to delete folder
14:49:07 : RemoveDirectory1 Error(2):C:\LGMobileUpgrade
14:49:07 : Start Date : 2012-10-12 14:49:07
14:49:07 : ---------- QM Testmode ---------
14:49:07 : ***** Check Tool Version *****
14:49:07 : Tool version : 1.5.4.8
14:49:07 : UpgradeDLL version : 1.2.6.7
14:49:07 : Current Dir : C:\ProgramData\LGMOBILEAX\B2C_Client
14:49:07 : LGE USB Driver Version :
14:49:07 : Android PDLV Version :
14:49:07 : Android NDLV Version :
14:49:07 : ******************************************
14:49:07 : [C:\ProgramData\LGMOBILEAX\Phone] Try to delete folder
14:49:07 : RemoveDirectory1 Error(2):C:\ProgramData\LGMOBILEAX\Phone
14:49:07 : SetEmerModeAT()
14:49:07 : _IsConnectedPhone Call
14:49:23 : _IsConnectedPhone(1)
14:49:23 : 0 - NotConnected.
14:49:23 : 1 - Normal connect success
14:49:23 : 2 - Emergency connect success
14:49:36 : *****CheckOS Start********
14:49:36 : Microsoft_Windows7_Professional_Service Pack 1
14:49:36 : *****CheckPCSyncPrograms Start*****
14:49:36 : PCSyncPrograms Not Found - OK and ready to upgrade
14:49:36 : Checking the connection with the cell phone...
14:49:36 : dwWaitResetTime(40000 ms)
14:49:37 : Phone Mode(1)
14:49:37 : *****GetPhoneType Start*****
14:49:37 : Phone Type : MDM_NVIDIA
14:49:37 : *****GetPhoneModel Start*****
14:49:38 : Phone read Model : LG-P999
14:49:38 : Server param Model :
14:49:38 : *****GetPhoneBinaryVersion Start*****
14:49:40 : CSE mode -> Version Replace
14:49:40 : *****Get ESN / IMEI / MEID Start*****
14:49:44 : Phone type Compare start
14:49:44 : *****Start _GetBatteryLevel*****
14:49:45 : Battery(4)
14:49:47 : *****CheckPCSyncPrograms Start*****
14:49:48 : PCSyncPrograms Not Found - OK and ready to upgrade
14:49:49 : ****************CheckAndDownload********************
14:49:49 : ******Extract Start C:\Users\adamskiii\Downloads\V21E_00.kdz*****
14:49:49 : Model Dll Dir(C:\ProgramData\LGMOBILEAX\Phone\)
14:49:49 : File Size = 186873893
14:49:51 : Extract kdz file Success.
14:49:51 : Extracted C:\ProgramData\LGMOBILEAX\Phone\\V21E.wdb\n
14:49:51 : WDB(or DZ) FullPath(C:\ProgramData\LGMOBILEAX\Phone\\V21E.wdb)
14:49:51 : Extracted C:\ProgramData\LGMOBILEAX\Phone\\Star_Model.dll\n
14:49:51 : Model dll FullPath(C:\ProgramData\LGMOBILEAX\Phone\\Star_Model.dll)
14:49:51 : NNNNN WDB FullPath(C:\ProgramData\LGMOBILEAX\Phone\V21E.wdb)
14:49:51 : NNNNN Model dll FullPath(C:\ProgramData\LGMOBILEAX\Phone\Star_Model.dll)
14:49:51 : Extract End C:\Users\adamskiii\Downloads\V21E_00.cab
14:49:51 : ------------------Model.dll Information-------------------
14:49:51 : Filename : Star_Model.dll
14:49:51 : Version : 1.0.0.8
14:49:51 : File size : 409600
14:49:51 : File date : 2011/08/31-09:43:46
14:49:51 : PC Created date: 2012/10/12-14:49:51
14:49:51 : ----------------------------------------------------------
14:49:51 : Connection check start........
14:50:07 : Check phone IMEI/ESN/MEID again.
14:50:07 : *****2nd ESN / IMEI / MEID check Start*****
14:50:11 : 2nd ESN/IMEI/MEID check : 0000000000000000
14:50:11 : IMEI Not match with first IMEI
14:50:11 : CLGMobileHttp Class ¼Ò¸ê½ÃÀÛ.
14:50:11 : CLGMobileHttp Class ¼Ò¸ê...
14:50:11 : Page_Error ºÎºÐÀÔ´Ï´Ù
14:50:11 : ¿©±â´Â Retry ºÎºÐÀÔ´Ï´Ù
14:50:11 : *****Check LGCM Programs Start*****
14:50:11 : LGCM Programs Not Found - OK and ready to upgrade
14:50:11 : *****WorkModelDLL Start*****
14:50:11 : strPhoneBinaryPath(C:\ProgramData\LGMOBILEAX\Phone\V21E.wdb)
14:50:11 : strModuleDir(C:\ProgramData\LGMOBILEAX\Phone\)
14:50:11 : strModelDLLPath(C:\ProgramData\LGMOBILEAX\Phone\Star_Model.dll)
14:50:11 : _DetachDLL Call
14:50:11 : _DetachDLL Call End
14:50:11 : Call fn_StartUpgrade
14:50:12 : ********* 2Chip Model.dll input Parameter*************
14:50:12 : MODEL_EVENT : 32769
14:50:12 : PhoneBinaryPath : C:\ProgramData\LGMOBILEAX\Phone\V21E.wdb
14:50:12 : ModuleDir : C:\ProgramData\LGMOBILEAX\Phone\
14:50:12 : BootWaitTime : 49500
14:50:12 : UsbHighSpeed : FALSE
14:50:12 : PhoneMode : 1
14:50:12 : NewPhoneBinVersion : V21E_00
14:50:12 : ClearSI : FALSE
14:50:12 : AuthMark : 0
14:50:12 : ********* 2Chip Model.dll input Parameter End*************
14:50:48 : wParam : 2010, lParam = 3036
14:50:48 : CleanModelDll() : Free Model.dll
14:50:48 : _DetachDLL Call
14:50:48 : _DetachDLL Call End
14:50:48 : Page_Error ºÎºÐÀÔ´Ï´Ù
14:50:48 : ¿©±â´Â Retry ºÎºÐÀÔ´Ï´Ù

Is there anything else I can try?