On recent FreeBSD, the tar binary has been replaced by bsdtar util. On old FreeBSD’s (8.2, 7.2 and more), the classic tar util is used. The problem is simple, tar cannot open lzma archives.
To resolve this problem (but you must resolve it with a freebsd-update !), here is a solution. You must install libarchive port and tell FreeBSD port tree to use the new bsdtar.
Here is the solution:
cd /usr/ports/archivers/libarchive
make install clean
Then edit /etc/make.conf and add the following line:
TAR=/usr/local/bin/bsdtar
That’s all !