firmware could not be updated

hi, i hvae a mac version 10.5.8 and i want to updet it to 10.6 to donlowd the new ituns and everithing, but in my software update only said i have to updet my bluethooth firewall, i tried but it keep telling me that: An unexpected error occurred (4:190). Your firmware could not be updated, please try again.what should i do?