He probably didn't do anything wrong. Deleting log files which have no function serves no purpose. There is an underlying problem. Restarting, rescanning and repairing seems to fix temporarily but the error always comes back. Sometimes after a few minutes sometimes after hours, sometimes after a re-start of the client. It's not the size of the log file that is a problem. If you start the client with full logging enabled the log file ends up ten times the size. It doesn't seem to stop the wallet working though. I've been getting stakes too, whilst the error is displayed but often when re-starting the wallet I end up with double my real balance until a further restart/rescan.........not too worried. It'll get resolved.