1st: need are the files that you get here:
https://mega.co.nz/#!3dRlySCT!czu3OV...ExS9EoW3wAOYCw
2nd: Install the LGUnitedMobileDriver
(first LGUnitedMobileDriver_S4981CAN36AP22_ML_WHQL_Ver_3[1].6 & 2nd LGUnitedMobileDriver_S4981MAN36AP22_ML_WHQL_Ver_3[1].6)
3: Turn Off your Mobile and remove your SD and Sim-Card
4: Press volumen down and put in your USB-Cable
5: When your computer detect, it installs the driver
6: After Driver installation, go to device manager select “LGE CDMA USB SERIAL PORT” right click properties then connection setting advanced and set to “com41″
7: After that run LG FlashTool
8: Select in DLL the x3_2008_v0.0.6.9.dll
9: In S/W select only the LGP880.dz file that i´ve added in dz and dll file folder
10: In Action Mode select Upgrade DL
11: in Connection Mode select USB
12: Click on OK
13: Click on Port COM settings (COM plug icon) and select 1 ( Unmark the numbers above )
14: Click start(The Port 1 window should appear READY)
15: Disconnects USB cable and wait 5 seconds
16: Press and hold voll down button in Lg P880 and connect USB cable
17: The update process will begin automatically after that release the Vol Up
18: When the progress reaches 100%, the mobile will power on and boots automatically into ICS!
19: Congratulation you´ve made it
20: Now u can Flash v20a again :P