Problem

Receiving the following error message after upgrading Team Calendar:

Diagnosis

Check if an expired license is being used for the Team Calendars for Confluence plugin.

Cause

The Team Calendar license's expiry date is dated before the Team Calendars plugin release date. For example:

1. Team Calendars for Confluence license has an expiry date of 2nd June 2015
2. Team Calendars for Confluence version installed has a release date of 3rd June 2015

Workaround 

• Use Team Calendars for Confluence evaluation license.

Resolution 

Resolution 1

• Renew Team Calendars for Confluence license.

Resolution 2

Downgrade the Team Calendar plugin to a version that was released  before the expiry date of the current Team Calendar license:

1. Verify Team Calendar version release dates
2. Uninstall the current Team Calendar version by navigating to Confluence admin >> Manage Add-ons >> Uninstall Team Calendar
3. Install the desired Team Calendar version manually by using the downloaded .obr file obtained in Step 1

   1. To upload an add-on:

      1. From the application's administration console, click the Manage add-ons link.
      2. Click the Upload add-on link at the top right side of the page.  
         The following dialog appears.
      3. Enter the location of the JAR or OBR file to upload using the file chooser or by specifying a network location by entering a URL.
      4. Click Upload. 
         A confirmation message appears when the add-on is successfully installed.
      5. If prompted, restart your application to have your change take effect.
4. If you still see the error message, please clear the plugin cache by referring to the link -  How to clear plugin cache