When users cannot access files or directories that they previously could access, the permissions or ownership of the files or directories probably has changed.
Frequently, file and directory ownerships change because someone edited the files as superuser. When you create home directories for new users, be sure to make the user the owner of the dot (.) file in the home directory. When users do not own “.” they cannot create files in their own home directory.
Access problems can also arise when the group ownership changes or when a group of which a user is a member is deleted from the /etc/group database.
For information about how to change the permissions or ownership of a file that you are having problems accessing, see Chapter 6, Controlling Access to Files (Tasks), in System Administration Guide: Security Services.