A forum user has encountered a problem trying to install nspr-devel. See https://www.centos.org/modules/newbb/viewtopic.php?viewmode=flat&topic_id=30915&forum=37 The 5.6 versions look older than the 5.5 updates to yum. Attempting to install using CentOS-Vault.repo [C5.5-updates] repo also fails. Looks like tru_tru has noted the issue on #centos-qa. Phil