Please forgive me for being tardy to the party (I brought beer, though...honest). But since this just happened to me today and since I was able to figure out at least one possible reason why this behavior occurs, I wanted to share it.

This error message can occur if the folder that contains your backup file has a space in the folder name. To solve the problem, replace the space with a dash (this may work with an underscore as well, although I haven't tried it).

E.g. if your folder path is C:\SQL Backups\, rename it to C:\SQL-backups\.

Hopefully this helps someone. That one little dash can make all the difference (it did for me, anyway.)