The file is empty
The job ran on time and copied a 0KB file, or a file that will not open.
Not sure the backup can be opened?
A successful backup message is not a file you can open. Essential, from RM4,500 a month, includes a restore test.
What we usually find
The external drive stopped
The letter changed, or the disk filled up, and nobody noticed.
SQL was left out
Shared folders were copied. AutoCount, SQL, or the ERP database was not.