Update 2.1.5 to 2.2 fails with PostgreSQL database: operator does not exist

When I try to upgrade our existing Bamboo 2.1.5 instance to version 2.2, the database upgrade fails with the following error message:

2009-03-11 09:58:34,059 INFO [main] [UpgradeLauncher] Current data is at build number: 1009. Upgrade required. Firing upgrade manager...
2009-03-11 09:58:34,102 INFO [main] [UpgradeManagerImpl] Found 2 high priority upgrade tasks
2009-03-11 09:58:34,103 INFO [main] [UpgradeManagerImpl] --------------------------------------------------------------------------------------
2009-03-11 09:58:34,103 INFO [main] [UpgradeManagerImpl] Running upgrade task 1101 : Converting Notification Rules to be one recipient per rule
2009-03-11 09:58:34,103 INFO [main] [UpgradeManagerImpl] --------------------------------------------------------------------------------------
2009-03-11 09:58:34,369 INFO [main] [UpgradeTask1101NotificationRecipients] Converting Notification Rules for MBADMIN-PGBACKUP
2009-03-11 09:58:34,370 INFO [main] [UpgradeTask1101NotificationRecipients] Converting Rule: com.atlassian.bamboo.plugin.system.notifications:buildCompleted.failedBuilds,
2009-03-11 09:58:34,399 ERROR [main] [UpgradeTask1101NotificationRecipients] Unable to update notifications: ERROR: operator does not exist: bigint = character varying
org.postgresql.util.PSQLException: ERROR: operator does not exist: bigint = character varying