I trying to recover the farm from backup.
Backup made with the same environment: Sharepoint 2010 + Nintex Workflow 2010 + SQL Server 2008 R2, restore the standard way in the Central Administration.
Object Nintex Live Forms Online Service failed in event OnRestore. For more information, see the spbackup.log or sprestore.log file located in the backup directory.
ArgumentNullException: Value cannot be null.
Parameter name: liveObject
how can I fix and restore the farm?
For your reference all backup/restore methods supported by us can be read here. Nintex Workflow Backup and Restore
In this case we would need to know as much as possible about the "standard" way followed. If you could outline how the back up is configured in detail. The steps in detail for the restore. It may help paint a clearer picture for us to comment on.
Personally I would recommend build a backup/restore plan around.