The stuff is that everytime you will create a new category, you may face this problem:
4images creates the category in the database, as it has permissions to do it.
But... 4images, as "Apache user", is not allowed by your host to create an upload directory with requisite premissions. SafeMode, PHPSUEXEC... most security issues explains the problem.
You will certainly have to manage your categories' permissions by FTP or Cpanel or whatever... to get them accessible in read/write mode.