[GoranTornqvist]

Already run /admincp/update_ban_dates.php before.

This is weird, if I add this row, just before the code you specified above:
$perpage = 10;

it works!!!

so the $perpage does indeed loose its value somewhere...maybe a typo, I don't know.

$perpage=$warn_opts['warnings_per_page'];
echo "warnings_per_page=".$warn_opts['warnings_per_page']."<br>";

Told me that $warn_opts['warnings_per_page'] is empty. Where is this variable declared, assigned?

Any other ideas?