Unable to create directories

All of a sudden, all my virtual server’s default users are able through ftp to upload files in the public_html folder, but not create new directories within it. Any help ??

What exactly are “default users”? What errors do you get when you try it (in the client and the ProFTPD log)? Have access rights or owner user/group of the public_html changed?

I have found the solution.
Using SFTP instead of FTP solved the issue.

Thank you