"Communications Breakdown" error when JIRA is not down.

Symptoms

1. You get the following error when trying to perform a workflow action with a screen even though JIRA is up.
   
2. If you open the transition in a new tab you are directed to a HTTP (HTTPS) page even though your original page was served using HTTPS (HTTP).
3. You have a HTTP proxy sitting in front of JIRA.

Cause

This is generally caused when the proxy sitting in front of JIRA forwards each request from HTTPS (HTTP) to JIRA as HTTP (HTTPS). For example this following Apache HTTPd configuration does this:

SSLProxyEngine on
ProxyRequests       Off
ProxyPreserveHost On
ProxyPass           /jira       http://localhost:8080/jira
ProxyPassReverse    /jira       http://localhost:8080/jira

In this case we have Browser -> HTTPS -> Apache HTTpd -> HTTP -> JIRA(Tomcat). The problem is that JIRA thinks the request is coming from the client as HTTP rather than HTTPS. This makes JIRA generate some HTTP based links rather than the correct HTTPS based ones. To fix this you will need to tell JIRA the protocol that the client is using. You can do this using the "scheme", "proxyName" and "proxyPort" properties in the HTTP Tomcat connector. See "Alternative configuration if HTTPS is terminated on the proxy server" section at http://confluence.atlassian.com/display/JIRA/Integrating+JIRA+with+Apache+using+SSL for details.