Symptoms

• Clicking on Wiki Markup tab or the Preview tab there is a brief flash of the progress icon but nothing happens.
• The Plugin Repository spins and results in the message "Invalid reply from server."

Cause

Apache HTTPd is not configured to handle UTF-8 characters.

Resolution

Check the document Running Confluence behind Apache. For those using Mod_jk refer to Configuring Tomcat's URI encoding as you may need to add the following configuration to your <apache>/conf/httpd.conf file:

JkOptions +ForwardURICompatUnparsed