Do you know what is the version of the PSN game you downloaded? It could be as easy as doing a region change/sfo edit.

gamesave of the psn is: NPEB00043
gamesave of my old disc: BLES00074

the problem is not a different region change but different version PSN vs RETAIL

what do you suggest?

Try using the tricks shown in this links, mainly what's shown in first one:
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thanks vreal, i don't have xploder, should i do something similar with cfw?

That first link I posted is clearly the thing you're looking for. Without Xploder/Game Genie I'm not sure how it works, but there must be a way with CFW.

I really need to make a dummy PSN account just to try out this stuff ehehehe Either way, Xploder is rather cheap so it could be an option for you.

Thanks dude, I'll give it a try...
from what i remember, doing with cfw through FTp will do the trick you pointed out with xploder.

Thanks again