We tried to setup Zend Optimizer on a server following these instructions:

... but got the following error:

[[email protected] ZendOptimizer-2.5.10-linux-glibc21-i386]# php -v Failed loading
/usr/local/Zend/lib/Optimizer-2.5.10/php-4.3.x/ /usr/local/Zend/lib/Optimizer-2.5.10/php-4.3.x/ undefined symbol: zend_open
PHP 4.3.2 (cgi), Copyright (c) 1997-2003 The PHP Group
Zend Engine v1.3.0, Copyright (c) 1998-2003 Zend Technologies with the
ionCube PHP Loader v2.5, Copyright (c) 2002-2004, by
ionCube Ltd., and
with Zend Extension Manager v1.0.7, Copyright (c) 2003-2005, by
Zend Technologies

Any ideas what went wrong and how to fix it?