<<during a restore of a firebird gbk on a fres installed system with the same firebird 2.5 cs server like the original server, I get
this error:
attemp to store duplicate value (visible to active transactions) inn unique index „RDB$Index_39“ Problematic key value is
(„RDB$ROLE_NAME“ = ‚RDB$ADMIN‘)>>

Usually caused (AFAIK) by a restore done with Firebird 2.1 or an earlier gbak, or if a Firebird 2.5 backup was
restored to Firebird 2.1, backed up and then restored on Firebird 2.5

On the original database you can do

DROP ROLE RDB$ADMIN;
COMMIT;

When you restore, gbak.exe should recreate the RDB$ADMIN role.

Paul