Step 1:

encoder_check.php

Invision Power Board Encoder Check

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PHP Version: 5.1.4 
PHP Operating System: Linux 
Zend Encoding Available? No 
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Which Trial Version Can I Use?
Zend is not available. You can use the IonCube encoded version. 

You will need to use the following loaders: 
PHP Version: Sorry, your PHP version isn't supported. Please see www.ioncube.com for more information. 
Running on: Linux

OK, what now? My PHP version is 5.1.4

you have to use IONCUBE

Yes, but I am confused.

I have uploaded via FTP all files, now address is www.mydomain.com/ipboard_ioncube

I got this: The file /path/ipboard_ioncube/sources/ipsclass.php has been encoded with the ionCube PHP Encoder and requires the free ioncube_loader_lin_5.1.so ionCube PHP Loader to be installed.

OK I am running under FreeBSD, I click on the http://www.ioncube.com/loaders.php and downloaded FreeBSD 4 (x86) Installer.

I have installed files to ipboard_ioncube/ioncube/ioncube

Is it correct? I feel that no. :unsure:

PHP 4.4.1 here, same problems reported above (with the encoder check). Host is sorting out encoding soon.

Required ZendOptimizer
http://www.zend.com/products/zend_optimizer

You must either ask you host to install Zend Optimizer (as stated) or have them give you a php option that is compatible with Ioncube. Outside of that, you will have to wait until the unencoded version. :)