Errors during make buildworld (5.4 to 6.0 upgrade)

[bsd at rio.com]

While running make buildworld after a make cleanworld and make cleandir in
attempts to upgrade from 5.4 to 6.0, I cannot get around the following
error:

make: don't know how to make /usr/src/lib/libalias/alias.c. Stop
*** Error code 2

Stop in /usr/src/lib.
*** Error code 1

Stop in /usr/src.
*** Error code 1

Stop in /usr/src.
*** Error code 1

Stop in /usr/src.
*** Error code 1

Stop in /usr/src.

I followed the suggestions from
http://www.nabble.com/buildworld-failing-on-amd64-with-RELENG_6-t494383.html
and although going into the directory in question and building there
worked, then running make buildworld quit at the same spot.
The only other report I have seen suggested rm -rf /usr/obj/*
(http://lists.freebsd.org/pipermail/freebsd-amd64/2005-November/006615.html)
but that is part of what make cleanworld does so I didn't feel the need to
do it yet again.

Any suggestions and help is welcome.

Cheers,

BSDuser