There's a compatibility issue with the Java Bridge in Zend Server CE which results in failure of the ZendServer admin interface. A temporary fix could be found at http://forums.zend.com/viewtopic.php?f=44&t=1115

I found this out the hard way - reinstalled and digged the internals before realizing it was a compatibility issue. I hope the Zend guys fix this soon!

Oh, I'm on Zend Server CE 4.0.5