Resolution:
When running a Manager on some versions of Linux, Engine Daemons never log in, and when attempting to access the Engine Daemon Admin page in the GridServer Administration Tool, it never completes loading and is unavailable.

This is a known issue in Java, and is documented in the following link: http://forums.sun.com/thread.jspa?threadID=230198&forumID=9

To correct this issue, update the java.security file on the Manager as described in the link above.