pkg method failed

[Arnab Bhowmick]

Today when i was downloading some package through pkg install method i git
the following output

root at arnab:/usr/home/ARNAB # pkg install opera
Updating FreeBSD repository catalogue...
FreeBSD repository is up-to-date.
All repositories are up-to-date.
The following 7 package(s) will be affected (of 0 checked):

New packages to be INSTALLED:
        opera: 12.16_6
        gstreamer-plugins-good: 0.10.31_2,3
        gstreamer-plugins-ogg: 0.10.36_1,3
        gstreamer-plugins-theora: 0.10.36_1,3
        gstreamer-plugins-vp8: 0.10.23_3,3
        gstreamer-plugins-bad: 0.10.23_2,3
        gstreamer-plugins-vorbis: 0.10.36_1,3

The process will require 53 MiB more space.
15 MiB to be downloaded.

Proceed with this action? [y/N]: y
Fetching opera-12.16_6.txz: 100%   13 MiB 109.3kB/s    02:04
pkg: cached package opera-12.16_6: size mismatch, fetching from remote
Fetching opera-12.16_6.txz: 100%   13 MiB 139.7kB/s    01:37
pkg: cached package opera-12.16_6: size mismatch, cannot continue
root at arnab:/usr/home/ARNAB #

Can anyone say that why i got this massage?