ERPNEXT Upgrade error

I tried to upgrade the ERPNEXT software. While performing final installs, it displayed the message something like “Update error, there is no running instance. If you are in development mode use bench start.” I started the bench and again tried to update but then it showed “Backup failed for site. Database or site_config.json may be corrupted” Please help! Also please let me know how to restore the previous backup. (I had taken the backup of database, site_config.json, public files and private files).