I got the following error for PHP after recent portupgrade:
PHP Warning: PHP Startup: Unable to load dynamic library '/usr/local/lib/php/20090626/memcache.so' - /usr/local/lib/php/20090626/memcache.so: Undefined symbol "php_session_create_id" in Unknown on line 0
to fix this all you need to do is reinstall pecl-memcache, like this:
cd /usr/ports/databases/pecl-memcache make deinstall make install clean
that should make the problem go away ...