[Koha] error generated by writing off fine

{UNKNOWN}: Can't call method "unblessed" on an undefined value at /usr/share/koha/lib/C4/Circulation.pm line 2181, <DATA> line 751. at /usr/share/koha/lib/C4/Circulation.pm line 2201 For help, please send mail to the webmaster ([no address given]), giving this error message and the time and date of the error. --- patron had a fine...patron paid part of fine....librarian "wrote off" the rest of the fine...when fine write off button was pressed ...this error message popped up. -S