Can a log fill if the disk it's on is not full?

On a couple of occasions, I got the exception
SQL Exception: Cannot write to the log, most likely the log is full.  Please delete unnecessary files.  It is also possible that the file system is read only, or the disk has failed, or some other problems with the media.
The filesystem where Derby resides is definitely not full or read only.  This occurred during shutdown of my app, although I cannot tell whether it happened before, during or after my DriverManager.getConnection("jdbc:derby:;shutdown=true") call.  It does not occur consistently and I haven't found a way to force it to occur.