Looks like your nmblookup alternatives definition file got corrupted (?)
You could try force-installing it again: sudo update-alternatives --force --install /usr/bin/nmblookup nmblookup /usr/bin/nmblookup.samba3 0 --slave /usr/share/man/man1/nmblookup.1.gz nmblookup.1.gz /usr/share/man/man1/nmblookup.samba3.1.gz
Also update-alternatives has been revamped in lucid, so this might be already fixed.
Looks like your nmblookup alternatives definition file got corrupted (?)
You could try force-installing it again: nmblookup. samba3 0 --slave /usr/share/ man/man1/ nmblookup. 1.gz nmblookup.1.gz /usr/share/ man/man1/ nmblookup. samba3. 1.gz
sudo update-alternatives --force --install /usr/bin/nmblookup nmblookup /usr/bin/
Also update-alternatives has been revamped in lucid, so this might be already fixed.