In my case,

cd /usr/pkgsrc
cvs update -r netbsd-1-6-1 -dP
cd pkgtools/pkg_install
make install

seems to have fixed it.

This was derived from the suggestion at 
http://news.gw.com/netbsd.help/26896, but the first time I did this it 
didn't help.  The second time it did, and now pkgsrc seems to function 
correctly.