Recovery file does not match db file

Just rebooted my production server, which had been running fine for months.
When it came up, these errors started:

ObjectDB 2.3.1_03] javax.persistence.PersistenceException
Recovery file '/auctionologies/java/storage.odb$' does not match db file '/auctionologies/java/storage.odb' (error 145)
  at com.objectdb.jpa.EMF.createEntityManager(EMF.java:176)
  at javax.persistence.EntityManagerFactory$createEntityManager.call(Unknown Source)

Note: other than reboot the machine, I didn't do anything else.

Any idea what's going on?

This may be related to issue 695, which has been fixed in version 2.4.0.

Please check if the recovery file (odb$) is empty, and if it is - just delete it and restart the database server.

Version 2.3.1 is nearly one year old - you should upgrade your server.

recovery files aren't completely empty (though are tiny, around 306 bytes).

confirmed that problem is resolved when the recovery files are deleted, does'nt seem to be any data loss.

not currently able to upgrade to the latest version, but will do so in the next release.

Dave