FreeBSD：Python 2.7をインストールできません。

私のFreeBSDシステムにPython 2.7をインストールできないようです。以下はいくつかの情報です。

# portsnap update
Ports tree is already up to date.

バージョン:

# uname -r
7.1-RELEASE

取付ける:

# cd /usr/ports/lang/python27/
# make
===>  Found saved configuration for python27-2.7.5_1
=> Python-2.7.5.tar.xz doesn't seem to exist in /usr/ports/distfiles/python.
=> Attempting to fetch ftp://ftp.lv.freebsd.org/pub/FreeBSD/distfiles/python/Python-2.7.5.tar.xz
Python-2.7.5.tar.xz                           100% of    9 MB  159 kBps 00m00s
===> Fetching all distfiles required by python27-2.7.5_1 for building
===>  Extracting for python27-2.7.5_1
=> SHA256 Checksum OK for python/Python-2.7.5.tar.xz.
===>   python27-2.7.5_1 depends on file: /usr/local/bin/xz - found
tar: Unrecognized archive format: Inappropriate file type or format
tar: Error exit delayed from previous errors.
*** Error code 1

Stop in /usr/ports/lang/python27.
*** Error code 1

Stop in /usr/ports/lang/python27.

どんな助けでも大変感謝します。