squirrelmail suddenly not working

Has something just been updated? Suddenly two clients have called complaining that the Squirrelmail version 1.4.9a is giving the following error message when they try to login:

ERROR
You must be logged in to access this page.
Go to the login page

They can access mail via a standard email client, but several clients are abroad and thus can only enter via the webmail interface, and thus are quite upset.

This has been working for several months now, so I'm wondering if something was recently updated that would require Squirrelmail to lose track of who is allowed to login or passwords, etc.

Can you please point me in the right direction?

Status: 
Closed (fixed)