my system is circulating books in yesterday date and i can't checkout books for some student it just give a yellow sign with no massage

You don't say which version you're using, but the second problem sounds like a bug which has been fixed for over a year: http://bugs.koha-community.org/bugzilla3/attachment.cgi?id=1794 If that is the same problem you're seeing you'll need to upgrade Koha. -- Owen -- Web Developer Athens County Public Libraries http://www.myacpl.org