wololo.net/talk

well i upgraded my psp from 5.50 prome 2 where you gonna change some text 9.90 to 5.50 (i dont much remember)
upgraded to 6.60 ofw and installed cfw pro c fix3 and it succeed. checked system info and it shows 6.60 pro c
but when i try to play games like:
tekken 6 = black screen
need for speed shift = 80020148 error

actions taken
set everything to default clock

so i wanted to downgrade to 6.20 but it shows same eror as need for speed shift

You probably have a bad copy of NFS. Try using different iso drivers, one of them may work. Or your games may have some patch that was needed to run on the older fw. Try making a new untouched backup, don't compress it to cso.
For downgrading, some people ,including me , have had better luck going from 6.60>6.3x>6.20 (with different downgraded each step I think) rather than directly to 6.20.