Thanks for trying to help guys.
I could fix this myself, i wanted to share this with you:
I made the database to read_only mode using gfix command and then the backup worked like charm. Then i restored the DB and changed the mode back to read_write!!!

--- In firebird-support@yahoogroups.com, Dimitry Sibiryakov <sd@...> wrote:
>
> > I am unable to recover data a corrupted .fdb file.
> >
> > The size of the daddb.fdb is 3.3 GB.
> >
> > I am on a timecrunch situation to resolve this ASAP.
>
> The only people that can help you are here: http://www.ib-aid.com/
>
> SY, SD.
>