Fix the checksum Audi A4 EDC16

I read the map of a' A4 2.0 16v 140 HP ECU EDC16 hw 113 sf 740. The car is mapped and it goes too, and the customer requests a downgrade. I read by OBD the file that I modified but write error RSA. I have run the read BDM but save a file with a CK wrong and the ECM can't correct it. I don't understand what kind of surgery was done, but if you correct the ck, and you rewrite the file, it should work. Maybe with the file ORI and I could solve even if you could find the without upgrade soft (03g906016GN 7004) ?
In the meantime, wonder if someone can correct the checksum on the file "bekup map" bed in BDM or better to make the dowgrade ( for the original) and fix the Check.
I think that was made a kind of protection of the map, if someone explains to me what can be done, just for curiosity , I would be grateful for the info.
Thanks

and best WISHES to all.

I see difficult if you do not find the original file..
however, the tools should correct the checksum in writing..

I have done some work on files being read on the serial line
the file "AUDI A4 MOD READ BY OBD.ORI" as it says in the extension and the original
the file "WinOLS (Audi A4 (down_boss_cks_ok) - 374970) and what to write with the downgrade, with cks correct.
the file"Audi a4 mod bed from OBD_boss" and what you read you serial modified and corrected for writing,

they have done no rather on the file , and only a matter of cks, try to write to me and tell me how it ends writing, (speaking of which, what to write the file?)
if you have any other problem just ask and let's solve it, time permitting.

Thanks Boss. Monday I try to write. I use a Kess clone , that reading is OK but writing it gave error RSA . Then with Ck correct you should have no problems?