Symptoms

When adding the JIRA Calendar to the Dashboard, selecting Due Date, Planned Start or Planned End in the "Date to Display" dropdown and generating the Calendar will result in:

An internal server error occurred when requesting resource http://example.com/rest/calendar-plugin/1.0/calendar/htmlcalendar.html?dateFieldName=duedate&displayVersions=true&numOfIssueIcons=10&context=gadget&portletId=10901&includeContainer=true&searchRequestId=10261.

The following appears in the atlassian-jira.log:

09-Aug-2012 16:33:19 com.sun.jersey.server.impl.application.WebApplicationImpl onException
SEVERE: Internal server error
java.lang.NoClassDefFoundError: com/atlassian/jira/timezone/TimeZoneManager

Cause

Incompatible JIRA Calendar Plugin with your version of JIRA

Resolution

1. Download the correct version of the JIRA Calendar Plugin from https://marketplace.atlassian.com/293

2. Uninstall the existing JIRA Calendar Plugin in your JIRA Administration >> Plugins

3. Install the newly downloaded JIRA Calendar Plugin via JIRA Administration >> Plugins >> Install Plugin