Clients with network home folders cannot log in

Hi all, I had to power down my network over the weekend, and since restarting I find that clients with network home directories cannot log in. I have set up my clients with photos that display on the client machine login screen and these have been replaced by the generic image. I get the error message that says "You are unable to log in the the user "ian" at this time"... etc. I see from searching that this was a common problem with 10.3.9 but I am running 10.4.9 everywhere, so I suspect a different cause. In any case I have tried a number of the fixes suggested at that time (such as clearing and restoring the Open Directory connection on the client, etc.) to no avail. One other odd thing. The Open Directory service pane in Server Admin shows the service being in an odd state: the Start Service button is green, but greyed out - i.e. I can apparently neither start nor stop the service. It is an OD Master. Can anyone suggest a good approach to isolating the cause of this problem? Thanks, Ian. --