"Apple has recently discovered a compatibility issue affecting owners of PowerBook 3400 systems who are also using At Ease 4.0.x.
The PowerBook 3400 Password Security and the At Ease 4.0.x security driver are not compatible and, if used in conjunction, will prevent the PowerBook 3400 from booting. All data on the internal hard drive may be lost. This issue should not affect any external drives connected to the PowerBook.
Customers should not, under any circumstances, enable the PowerBook 3400 password security if At Ease 4.0.x has been installed on the PowerBook and the "Prevent users from bypassing security by starting up from a floppy disk" option in the At Ease administration program has been enabled.
Apple is working on a solution. Updates to this issue will be in the Apple Tech Info Library."