nis somehow doesn't start on boot

[johannes <johannes121@gmx.de>]

I have a sarge installation on several workstations. I don't know how it 
happened, but on one of them nis doesn't start automatically on boot. 
I've already tried

aptitude purge nis
aptitude install nis

to get back to a clean install, but it just doesn't work. Where should I 
look?

yp.conf contains
ypserver 192.168.0.24

Thanks for reading this.
Johannes