this may have to do with the default php5 installation. It is inherently more secure than php4 so several functions are disabled by default. What version are you running? I am running 5.2.6
System Linux integramod.com 2.6.18-1.2257.xxx #1 Fri Dec 15 16:06:24 EST 2006 i686
Build Date Nov 16 2008 08:30:34
Configure Command './configure' '--disable-pdo' '--enable-bcmath' '--enable-calendar' '--enable-exif' '--enable-fastcgi' '--enable-ftp' '--enable-libxml' '--enable-magic-quotes' '--enable-sockets' '--enable-zip' '--prefix=/usr' '--with-bz2' '--with-gd' '--with-gettext' '--with-imap=/opt/php_with_imap_client/' '--with-imap-ssl=/usr' '--with-jpeg-dir=/usr' '--with-kerberos' '--with-libxml-dir=/opt/xml2/' '--with-mysql=/usr' '--with-mysql-sock=/var/lib/mysql/mysql.sock' '--with-mysqli=/usr/bin/mysql_config' '--with-png-dir=/usr' '--with-xpm-dir=/usr' '--with-zlib' '--with-zlib-dir=/usr'
Server API CGI/FastCGI
Virtual Directory Support disabled
PHP API xx
PHP Extension xx
Zend Extension xx
suhosin xx
Debug Build no
Zend Memory Manager enabled
IPv6 Support enabled
Registered PHP Streams zip, php, file, data, http, ftp, compress.bzip2, compress.zlib
Registered Stream Socket Transports tcp, udp, unix, udg
Registered Stream Filters string.rot13, string.toupper, string.tolower, string.strip_tags, convert.*, consumed, convert.iconv.*, bzip2.*, zlib.*
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