If you are using File to Tape in Veeam 8.0 and you receive this "Error code: 123 Failed to open file" (Warning backup) the solution is remove the \ at the end
Task \\srv\backup\ completed with warning. Details: La sintassi del nome del file, della directory o del volume non � corretta. Error code: 123 Failed to open file [\\srv\backup\] in readonly mode.
If you are adding a new folder in Veeam 8 it will be automatically removed. The problem is if you have upgraded from Veeam 7.x
The right folder is "\\srv\backup" and not "\\srv\backup\"