Back-up failing to write to a UNC path the following error is generated: 50053 : The Network path was not found. LiteSpeed could not open the backup file.
The SQL Server service is running as Local System and cannot see that path location.
Backup to a local directory on the SQL Server machine or else utilise a domain account for the SQL Server service to run under. Make sure that user account has sufficient privileges to read and write to the backup destination through the path given (SQL Server does not support mapped drives).