Time stamp is in the future when running a backup

Hi

When running a backup I’m getting the following error;

/bin/tar: var/www/html/admin/assets/images/jquery-ui/ui-icons_3d80b3_256x240.png: time stamp 2013-04-29 23:34:15 is 9193.998187021 s in the future
/bin/tar: var/www/html/admin/assets/images/jquery-ui/ui-icons_2e83ff_256x240.png: time stamp 2013-04-29 23:34:15 is 9193.998163019 s in the future
/bin/tar: var/www/html/admin/assets/images/jquery-ui/ui-icons_72a7cf_256x240.png: time stamp 2013-04-29 23:34:15 is 9193.997822618 s in the future

That time stamp is in the future (its 21:00 here now). The time and date on the server is correct.

Any ideas?

Olly