Mac OS X Managed Client: "You are already logged on to another computer" Message

Symptom

A user who tries to log in at a second computer after the first stops responding sees this message:

"You cannot continue because you are already logged on to another computer. You may only log into one computer at a time. Contact your system administrator for help."

Solution

Use one of these methods:

• Have the user log back into the server on the same client computer that stopped responding. You may need to force the client computer to restart.
  
• Use the Server Status application to manually disconnect the user's AFP connection. If the user has multiple sessions open from the same client computer, disconnect them all.

Note: If this issue affects only 10.4 clients, it may be due to access to the invisible folder ~/.Spotlight-V100. The issue would happen if the owner of this folder were set to read-only permissions, for example. The owner of this folder must have full read-write-execute permissions ("rwx" or "7"). Files inside ~/.Spotlight-V100/ must be set to read-write ("rw" or "6"), with exception of mds-lock-dir and slave-work-dir, which should be set to rwx.