[System.ObsoleteAttribute(@"As of version 8.0 please use GetCommitTimestamp() instead.")]
long GetVersion()

returns the transaction serial number ("version") the referenced object was stored with last. Version number generation has to be turned on, in order to be able to use this feature: Db4objects.Db4o.Config.IFileConfiguration.GenerateVersionNumbers(Db4objects.Db4o.Config.ConfigScope)
This feature was replaced by Db4objects.Db4o.Ext.IObjectInfo.GetCommitTimestamp . The main difference is that the old version mechanism used to assign a serial timestamp to the object upon storing time, and the new commitTimestamp approach, assigns it upon commit time.