[HELP] how to flash stock rom using a custom rom installed in novo 8

i have installed a custom cyanogen rom with twrp on my ainol novo8 discover quadcore tablet.
I always use PAD product tool to upgrade roms or to flash if the rom crashed.

BUT after installing the cyanogen rom I am unable to flash a stock rom on it...
It stucks at 26% and error displayed DOWNLOAD_VMLX1_FAILED.
You can also take a look i the attached screen shot.

Please help me to fix this issue because I am done with cyanogen rom... :(
:eek: :(

Download from this link