My tar can unpack that file just fine, I'd guess your download simply aborted prematurely.

In case you want some data for comparison:

$ sha1sum perl-5.14.2.tar.gz
df1549d65cdef2b20023af83ecaa2a024109a5ad  perl-5.14.2.tar.gz
$ wc -c perl-5.14.2.tar.gz
15223598 perl-5.14.2.tar.gz
[download]