Users Fails logging out

We have multiple machines that have problems logging out.

When a user logsout, the message say's logout is not possible because running app is not quiting.

Even when al apps are clossed. Only thing to do than is :

- hard restart from ARD

- shutting down by pressing on/off button

- quit the windowserver from the Activity Monitor

Running Mac OS X !0.5.8 and Mac OS X Server 10.5.8.

What i have done :

- cache cleaning

- permission repair

- disk check

When this happens also the function key's for dashboard and expose are not working anymore.