If you manage your server remotely, you can create a directory structure beyond the 256 character MAX_PATH. If you subsequently logon locally and use explorer, you will receive the subject messages.
If you try to create a new folder, you may receive:
Unable to create the folder <name>.
The filename or extension is too long.
To fix the problem, navigate to the immediate parent folder and choose View / Details. In the right hand pane, click the folder that returned the error and rename it to make it shorter. You may also rename higher level folders.
This message can also appear if the user does not have access to their profile folder.