Whilst playing with Zend Server Community Edition trying to get mySQL to work I found myself at a point where mySQL would not start.
sudo zendctl.sh start-mysql
Starting MySQL
. ERROR! Manager of pid-file quit without updating file.
I had tried removing ZEND Server completely as documented on the Zend site. At best this is a bit vague.
- Stop all Zend Server processes
- Delete all Zend Server installed files
- Remove the .app from /Applications
- Remove Zend users
No matter what I did I always got the same error after re installing. So after looking round the file structure I tried running a script called uninstall located in the Zend bin folder. This asks a few questions but after completing the process and re installing, then all now seems to work 
Robs-MacBook-Pro:bin rob$ sudo /usr/local/zend/bin/uninstall.sh
Are you sure you wish to completely remove Zend Server? [yes|no]
yes
Stopping Zend Server 5.5.0 ..
httpd: Could not reliably determine the server's fully qualified domain name, using Robs-MacBook-Pro.local for ServerName
/usr/local/zend/bin/apachectl stop [OK]
Stopping Zend Server GUI [Lighttpd] [OK]
ERROR! MySQL manager or server PID file could not be found!
Stopping Java bridge [OK]
Zend Server stopped.
/usr/local/zend/apache2/htdocs and /usr/local/zend/mysql will be removed during this operation, if you wish to backup your PHP code and MySQL DBs,
please do so now and type "cont" to continue.
cont
Robs-MacBook-Pro:bin rob$