A CHECKSUMS file is in each CPAN author directory; for
example, see
http://www.cpan.org/authors/id/G/GR/GRANTM/.
They are generated automatically, and from some
random browsing of recent arrivals, appear to be
updated about 3 hours or so after the
latest release in a particular directory.
So in principle there may be a time delay present
between a distribution and it's appearance in the
CHECKSUMS file. However,
XML-Simple was
last updated on 29-Jan-2005, and the CHECKSUMS
file at
www.cpan.org is dated 11-Nov-2005, so there
shouldn't be a problem in this respect. This probably
means you're either using an out-of-synch mirror or
there was a problem in the network transfer.