Angry [Q] How to downgrade LG optimus 2x from cyanogen to gingerbird stock rom

I have LG optimus 2x P990 handset, I have rooted this phone via one click recovery. After that i install cm-10.1-20130915-NIGHTLY-p990 custom rom ang got android 4.2.2. I forgot to take a backup of previous image. cyanogen doesnt support native video calling without data. Handset problem also occur. Please help me to restore my phone back to stock ROM. When I tried to restore the backup from external card it shows md mismatch. I dont know now what to do .please help.