I think i resolved the problem.
In Nero i had activated the "write short leadout" option (in the expert-settings dialog) due to some bug with overburning (Nero 184.108.40.206 rejected overburning unless this option was set, even when the max. overburning size was set to 99 minutes). In Nero 220.127.116.11 the bug was resolved and i deactivated this option. Now it works with enabled GigaRec without any errors.
CloneCD still presents the same error message. Perhaps it uses short leadouts by default.
Thank you for your answers!