We have a website maintained by an old employee and it appears it's encoded by Zend Guard including all backups.
I know a little about Zend Optimizer, but never considered it for source protection as I know in the end the bytecode will need to be decoded for the interpreter, and was sure people easily decode optimized files using some software.
Now I need to decode some files and I can't find anything but some 'paid services'. We have the ownership of the code and are locked out now for any changes and debugging. How can I decode our files back?
The entire point of the very expensive software tool Zend Guard is to encrypt code so that it can not be decoded. That is the point.
If obfuscation is not on, then there is a possibility that you may be able to get a professional to get the code back, less comments and formatting by means of hacking the code engine. If obfuscation is on, then it's easier to rewrite it to be honest.
Have a read of this article from the Zend site, I know it is a biased source but they are right: http://forums.zend.com/viewtopic.php?f=57&t=2242