PCRE has not been compiled with Unicode property support.

http://www.php.net/pcre

The simplest solution is to rebuild the RPM

pcretest -C
PCRE version 6.6 06-Feb-2006
Compiled with
  UTF-8 support
  No Unicode properties support
  Newline character is LF
  Internal link size = 2
  POSIX malloc threshold = 10
  Default match limit = 10000000
  Default recursion depth limit = 10000000
  Match recursion uses stack

A source RPM should be available at ftp://ftp.redhat.com/pub/redhat/linux/enterprise/5Server/en/os/SRPMS/

rpm -ivh pcre-6.6-2.el5_1.7.src.rpm

Just change:

%configure --enable-utf8

%configure --enable-utf8 --enable-unicode-properties

/usr/src/redhat/SPECS/pcre.spec

Now rebuild, install and restart Apache

rpmbuild -ba /usr/src/redhat/SPECS/pcre.spec
rpm -Uvh /usr/src/redhat/RPMS/i386/pcre-6.6-2.7.XX.rpm

PCRE version 6.6 06-Feb-2006
Compiled with
  UTF-8 support
  Unicode properties support
  Newline character is LF
  Internal link size = 2
  POSIX malloc threshold = 10
  Default match limit = 10000000
  Default recursion depth limit = 10000000
  Match recursion uses stack