At session startup the X environment (specifically the 'xauth' utility) needs to lock the authority files.

If this operation cannot be accomplished, the X environment can't be setup properly and the session won't start.

The reasons can vary. The problem was originally reported by users running Novell Netware 6.0 in conjunction with NFS-mounted home directories.

Novell NFS supports file locking on traditional volumes in Netware 6, but on NSS volumes you need Netware 6.5 for file locking. Without file locking xauth doesn't work and so X won't start. If you want X sessions, you have the choice of using non-NFS home directories or upgrading your Novell Netware to 6.5.