Summary of problem:
If you install Express Server on a machine with version 1.8 of the Java Runtime Environment, you will not be able to access the Express Server Manager or ExpressZip web applications. If you navigate to one of the web application in a web browser, the application will not load and you may receive a message that the web page is not available.
If you upgrade to version 1.8 of the Java Runtime Environment after installing Express Server, you will still be able to access existing Express Server imagery by means of WMS. However, the Express Server Manager and ExpressZip web applications will not be accessible.
Update: This issue is fixed in version 9.0.6 of Express Server. For more information, see Upgrading to Java 8.
The Express Server Manager and ExpressZip web applications require version 1.7 of the Java Runtime Environment. Remove version 1.8 of Java and install version 1.7.
On Windows, install the Oracle Java Runtime Environment. On Linux, install the OpenJDK.