Thank you. As I can see, your full file path+name is: "F:\My Documents\AMNO BACKUPS 12.3.18\AllMyNotes Documents.ddb - backup 16-02-28 .ddb - backup 16-03-01.ddb - backup 16-04-18.ddb - backup 16-07-16 .ddb - backup 16-11-08 JAN21.ddb - backup 17-07-07 .ddb - backup 18-02-27.ddb - backup 18-03-13.ddb"
Whole file path+name length is 255 characters. Windows has a limitation on file path+name length - MAXIMUM 255 characters! Aside that so long name and location is unusual and has no sense, a backup of it simply cannot be created as there is no way to add a single character to it.
So the solution would be very simple. Use menu item File -> Save As... and rename the file to simply "AllMyNotes Documents.ddb", also make sure to change the directory to "F:\My Documents\", please do not store main data file and its backups in the same folder. It's even highly recommended to store backups on different drives (if only possible), to survive hard disk failures.
P.S. I do not know why your data file name got so long and messy, possible it's somehow related to the fact that it's stored in the folder where only backups are supposed to be. Let me know if the issue will come back again, we'll investigate it.