Hi,

>why it's happenning after a backup and restore operation?
>I tried it more than once and the same error occurred.
>Does anybody have some ideas about it?

Did you backed it up using an older FB version and restored it using FB 2.1?

FB 2.1 has some changes in character sets so that a 'migration' may need a
metadata update (as stated on release note/migration docs)


Regards,
Anderson