Mick and I just ran through this issue with my webhost. This is what I had to do, I'm not sure if your host is setup the same way, but give this a shot and see if it works.
What is Zend Optimizer and how do I set it up?
The Zend Optimizer is a freeware tool for parsing pre-compiled PHP files. These PHP
files must first have been compiled with the Zend Encoder which however is not a
freeware. The advantage of pre-compiled files is that they do not need to be parsed
repeatedly and therefore execute faster.
Please note
In order to install the Zend Optimizer you require SSH access. And only certain
packages have SSH (Check FAQ What packages support SSH Access?
Follow instructions from FAQ How to connect using ssh? - Didn't have to use this actually1. Download the Zend Optimizer from
http://www.zend.com/store/products/zend-optimizer.php (for Linux glibc 2.1)
2. Unzip the files locally on your computer. (tar -xvzf "the tar file")
3. Go to the directory where the Zend Optimizer has been unpacked. Go to "data"
directory. Here you can see various directories named according to PHP versions, e.g.
4_4_1_comp. Go the the directory of your choice. The important file is
"ZendOptimizer.so"
5. Upload this file into a directory of your choice within your webspace.
6. Change the php.ini file to include the following text:
zend_optimizer.optimization_level=15
zend_extension=/homepages/12/d1234567/htdocs/ZendOptimizer.so
Note that you will need to use your path name "/homepages/xx/dxxxxxxx/htdocs/ to
your webspace. You can find out the path name either via your 1&1 Control Panel,
under "Domains" or from the shell itself by entering the command "pwd"
All this info pulled from
1and1 FAQ's