A forum user has encountered a problem trying to install nspr-devel.
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.
Grokbase › Groups › CentOS › centos-devel › April 2011