Pathnames longer than 256 characters not supported [SOLVED]

The “pathname” refers to the full name of the file including it’s directory (also known as it’s “fully qualified file name”)
For example, a file called “test.mp3” that is in your Documents folder has a fully qualified file name of:
/Users/<your user name>/Documents/test.mp3

The maximum number of characters allowed in a fully qualified file name is determined by the operating system and the format of the “storage medium” (the hard drive / USB drive / wherever the file is stored).

The likely cause in your case is that you are trying to save the file into a folder that is nested in many levels of folders, so that the total length of the file path is close to the 256 character limit even without the name of the file.

The solution is to save the file to a shorter path, or use a drive that supports longer file paths.