database is already in use by another process

On startup confluence reports that the database is presumably locked by another process. There are extensive exceptions and the context does not start

2006-05-22 00:17:15,500 INFO [com.atlassian.confluence.lifecycle] contextInitialized Starting Confluence 2.2 (build #512)
2006-05-22 00:17:18,623 WARN [sf.hibernate.type.CustomType] <init> custom type does not implement Serializable: class org.springframework.orm.hibernate.support.BlobInputStreamType
Initializing c3p0 pool... com.mchange.v2.c3p0.PoolBackedDataSource@f186b8 [ connectionPoolDataSource -> com.mchange.v2.c3p0.WrapperConnectionPoolDataSource@1b7b32c [ acquireIncrement -> 1, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, idleConnectionTestPeriod -> 100, initialPoolSize -> 0, maxIdleTime -> 30, maxPoolSize -> 15, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 0, nestedDataSource -> com.mchange.v2.c3p0.DriverManagerDataSource@1571dff [ description -> null, driverClass -> null, factoryClassLocation -> null, jdbcUrl -> jdbc:hsqldb:/data/www/_webapps/confluence-data/database/confluencedb, properties ->

] , preferredTestQuery -> null, propertyCycle -> 300, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, usesTraditionalReflectiveProxies -> false ] , factoryClassLocation -> null, numHelperThreads -> 3, poolOwnerIdentityToken -> f186b8 ]
java.sql.SQLException: The database is already in use by another process: org.hsqldb.persist.NIOLockFile@8ef1a6b7[file =/data/www/_webapps/confluence-data/database/confluencedb.lck, exists=true, locked=false, valid=false, fl =null]: java.lang.Exception: checkHeartbeat(): lock file [/data/www/_webapps/confluence-data/database/confluencedb.lck] is presumably locked by another process.
at org.hsqldb.jdbc.Util.sqlException(Unknown Source)
at org.hsqldb.jdbc.jdbcConnection.<init>(Unknown Source)
at org.hsqldb.jdbcDriver.getConnection(Unknown Source)
at org.hsqldb.jdbcDriver.connect(Unknown Source)
at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:68)
at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:87)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1.acquireResource(C3P0PooledConnectionPool.java:83)
at com.mchange.v2.resourcepool.BasicResourcePool.assimilateResource(BasicResourcePool.java:884)
at com.mchange.v2.resourcepool.BasicResourcePool.acquireUntil(BasicResourcePool.java:601)
at com.mchange.v2.resourcepool.BasicResourcePool.access$400(BasicResourcePool.java:31)
at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1079)
at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:354)