nfs -device is busy- error

When attempting to log into a server from a kdm login screen to an nfs server, the login stops part way through when loading kde from the server. The error when doing a rcnfs reload is: /home: device is busy The only way to get the client back up to try and relogin is to go to runlevel 6 and reboot. Can anyone help? I think it's toi do with timeo in fstab but I'm not sure. what causes this error? Thanks, Steve.