With restoring a backupfile in FB 1.0

I have the following error message

gbak: creating indexes
gbak: ERROR: attempt to store duplicate value (visible to active
transactions) in unique index "RDB$PRIMARY10"
gbak: Index "RDB$PRIMARY10" failed to activate because:
gbak: The unique index has duplicate values or NULLs.
gbak: Delete or Update duplicate values or NULLs, and activate index with
gbak: ALTER INDEX "RDB$PRIMARY10" ACTIVE;

Does anyone have an idea how the backup file can be restored ?

Tanno