Total Finder 1.6.18 Refuses to copy files with .NB extension

I have an application called NoteBook. It creates files with an .nb extension.
At the end of each month, one of my backups is to a thumb drive. Prior to 1.6.18 there was no problem. Now I get a message that it can’t copy these files.
I have Yosemite 10.10.3.