Upgrading to Jira 5.1, I got the following error: "Gadget Dashboard bundled plugin is not available Error When Accesing JIRA" after completing the Jira installation. This makes Jira unusable. I resolved the problem by increasing the amount of PermGen space for the Tomcat server running Java. Below are my JAVA_OPT environment variable settings:
The values for Xmx, Xms, and MaxPermSize should all be adjusted for the size of your host server's memory.