Symptoms

Confluence does not start.

The following appears in the atlassian-confluence.log:

ERROR [main] [confluence.search.lucene.ConfluenceSearcherInitialisation] initialise Error encountered while warming up searcher: LUCENE_31
java.lang.NoSuchFieldError: LUCENE_31

Cause

This error usually happens due a corrupted installation directory.

Resolution

1. Shutdown Confluence
2. Create a backup of the entire Confluence installation directory
3. Download a new standalone zip file (same version of your current Confluence)
4. Extract it
5. Replace the current installation directory with the newly extracted files. However please keep the following files from your current installation directory and replace the ones in the new installation directory with them:
   server.xml located in <CONF_Install_Dir>/conf/
   confluence-init.properties located in <CONF_Install_Dir>/confluence/WEB-INF/classes/
6. Restart Confluence

If you face any problems regarding plugins, please clear your plugin cache.