Clients randomly freezing on boot - nfsmount: need a path

[Krsnendu dasa]

I am getting random errors booting clients from Edubuntu Feisty.
Most boot ok but some freeze just after the bar begins to fill up.
Clicking alt-ctrl F1 shows that the error is
nfsmount: need a path
It also sometimes has a white square instead of a file name next to
filename:

This cycles endlessly and the client doesn't get to the login screen.
Some clients seem to work if I try again, but others don't work no
matter how many times I reboot the client?

Any clues? Network problem? Client hardware? client RAM?

Thanks.
Krsnendu dasa