xauth package can't find libXau.so.6

On a fairly fresh amd64 7-current system (nothing X-related installed yet),
I installed this tightvnc package:

ftp://ftp.freebsd.org/pub/FreeBSD/ports/amd64/packages-7-current/net/tightvnc-1.3.8_2.tbz

This pulled in libXau and xauth packages.  However, whenever I run xauth (as
root or not), I get this error:

/libexec/ld-elf.so.1: Shared object "libXau.so.6" not found, required by
"xauth"

The file /usr/local/lib/libXau.so.6 does exist.

I have tried removing both libXau and xauth and reinstalling the packages (I
cannot install them from source because I get errors like this: /usr/bin/ld:
skipping incompatible /usr/local/lib/libXau.a when searching for -lXau)

This is my first post here, so I'm sorry if I didn't follow the, erm,
protocol for posting :)

- Phil