My backups stopped functioning. The error message says problems were encountered when attempt to create the folder for the backup. I looked at a list of folders and files on the backup drive and discovered a "package" from a few days ago with an inProgess extention. I tried to drag it to Trash without luck. Then, reading a suggestion (by @grgarside) to another user with - seemingly - the same issue, I went to Terminal and executed the suggested tmutil listbackups command, but the inProgress package did not appear in the resulting list (perhaps because it's a package rather than a file?)
Despite its path not being listed, I continued to follow the suggestions of @grgarside and executed the sudo tmutil delete /path/to/backup.inProgress command (replacing "path/to" with the path shown on my backup drive), but the result was this: No such file or directory (error 2)
Any suggestions? Please note that I'm a total novice. I had never heard of sudo nor tmutil until reading this thread.