I was wrong - FW/LW works fine
 

Accepts my queryHit with the calculated sha1 and asks for the file and i even finish DL, and the file is fine. I don't know what the f#$% is gtk-gnutella's problem with this sha1, but i can't keep hitting my head against that wall (metaphoric wall, of course, i took my pills today!).
So the file is fine - just gtk-gnutella doesn't allow me to give this sha1 for some reason.

Thanks for your always-rapid response, and of course your help.
If i ever will be able to find why gtk-gnutella doesn't accept this sha1 i'll post it.

Are you sure the SHA1 isn't listed in ~/.gtk-gnutella/done.sha1 or ~/.gtk-gnutella/sha1_cache?

Genious! why didn't i did what you suggested
 

earlier?! well, i finally found the done.sha1 file and found SO many occurences of the sha1 i wanted, since i DLded without a sha1 before and it calculated it.

Thanks alot. Now everything is fine, besided me feeling stupid for the time spent on this.

Can't thank you enough - now i can move on to other problems i have here and get on with my life.