[Koha] Barcode error

hello when staff put the item in the koha through catologue it gives the error message , barcode error , i opted to use accession number as barcode so as to avoid duplicate of data in the system but when i search in the database i will found the item with the callnumber , but when i try to search using callnumber or accession number (barcode) in normal way in koha i will not see the item -- regina