[Koha] Can't call method "as_usmarc" on an undefined value at /usr/share/koha/lib/C4/Search.pm koha

I use koha 3.02.03.000 on ubuntu 10.10 I exported the biblios using marc export tool when i search catelogue some times i get the error Can't call method "as_usmarc" on an undefined value at /usr/share/koha/lib/C4/Search.pm koha I am using nozebra. -- Priyadarsan K. P. --------------Official Address------------ Lecturer in Mathematics, C. K. G. M. Govt. college, Perambra P. O., Kozhikode Kerala, 676525-PIN       919496166465 Mob       914962610243 off http://ckgmgovcollege.homelinux.com --------------Residential Address------------ Karattillam "Supriya", Kottur P. O. Naduvannur, Kozhikode-673614, Kerala, India. Ph: 91496 2652330