Can not update png on 8.2-RELEASE-p9 amd64

[Hans de Hartog]

   Title says it all. WITH_PKGNG=yes. Error message:
   ===>  Extracting for png-1.5.16
   => SHA256 Checksum OK for libpng-1.5.16.tar.xz.
   => SHA256 Checksum OK for libpng-1.5.16-apng.patch.gz.
   tar: Unrecognized archive format
   tar: Error exit delayed from previous errors.
   *** Error code 1
   No problems on my other boxes (9.1-RELEASE i386).
   TIA,
   Hans