[Q] Error while flashing a CM based ROM after downgrading to KK from 5.0 topic

So, I had Asia 5.0.2 and I saw a FIUI ROM for our device at the MIUI forums. I decided to give this a go and first downgraded to KK and then tried to flash the zip from TWRP and Philz recovery but got this error:

"Can't install this package on top of incompatible data. Please try another package or run a factory reset"

I thought it might be a ROM specific error, but I also tried to flash CM11 but got the same error. How can I get around this? Is this an issue with the updater script or something?

Any help will be appreciated.