On upgrading this error was displayed:
Warning: Invalid argument supplied for foreach() in /home/*mysite*/public_html/wp-content/plugins/backupwordpress/functions/core.php on line 38
On deactivate/reactivate this error was displayed:
The plugin generated 179 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.