To clarify, this is not within a browser, it's within a system's GUI for copying files from one location to another.
I get this all the time when moving files around on Windows. A too-deep directory structure can cause it too. What I don't like about it is it doesn't specify **which** files/directories are too long.
We're all spoiled. Who remembers the 8/3 rule? :-) Pre Windows 95, you could only name files with names 8 characters long and a three character extension.