Symptoms

1. You are upgrading from Confluence 3.4.x directly to Confluence 4.x or above.

2. The following error appears in the UI indicating upgrade failure:

   You cannot access Confluence at present. Look at the table below to identify the reasons.
   
   
   Upgrade failed. Please consult the system logs for details. You will need to fix these problems, restore your database and confluence home directory to the pre upgrade state. Then retry the upgrade.

3. The following appears in the atlassian-confluence.log:

   2012-03-22 10:46:33,471 INFO [main] [confluence.upgrade.ddl.HibernateDdlExecutor] executeDdlStatements Executing DDL: drop index attch_idver_idx on ATTACHMENTDATA
   2012-03-22 10:46:33,596 ERROR [main] [atlassian.confluence.upgrade.UpgradeLauncherServletContextListener] contextInitialized Upgrade failed, application will not start: Upgrade task com.atlassian.confluence.upgrade.upgradetask.AddUniqueAttachmentIdConstraintToAttachmentDataUpgradeTask@a6cdf5 failed during the SCHEMA_UPGRADE phase due to: StatementCallback; bad SQL grammar [drop index attch_idver_idx on ATTACHMENTDATA]; nested exception is java.sql.SQLException: Cannot drop the index 'ATTACHMENTDATA.attch_idver_idx', because it does not exist or you do not have permission.

Cause

This error is typically caused when trying to upgrade from a pre-3.5.x version directly to 4.x. This bug has been filed here: CONF-27597 - Getting issue details... STATUS

Workaround

Try upgrading to 3.5.17 first as an intermediate step prior to going to 4.x.

Resolution

The relevant bug ( CONF-27597 - Getting issue details... STATUS ) has been resolved in Confluence 4.3.7. You will no longer run into this issue when upgrading directly to this version or above.