FLASHING ERROR AT THIS POINT? If you have installed JB before then your flashing may stop at 4% to 14%. This may be due JB rom already installed before or due to driver not completely installed for "SW Upgrade Mode".
WORKAROUND: Cancel flashing by exiting LG Update Tool. Phone should be still in SW Upgrade Mode, Remove USB Cable, wait 10 seconds, Insert USB cable again and let all drivers install for this mode. The device manager should look LIKE THIS SCREENSHOT. START AGAIN FROM STEP 6 (Read about Post-JB Issue)