I have this job on maintenance plan of SQL Server 2014 SP3 which backup "All databases" to a shared file of another server, but one database failed due to an error shown on my screenshot below. Note that the rest are successful and they are just using the same path, all databases are simple except for model which is full.
I think file path is the issue. As per the screenshot attached there is a space between your file path, which is causing error in creating as proper file path not found
Fix this and then try again, one more possibility is path not found please make sure that file path is correct. I did the same at my end and found same error code 3
as mentioned in your screenshot.