The expiering of cookies it not something you set.
It is an attribute that can be set on a cookie when writing it on the client PC via ASP (and would think PHP is the same, but have never worked in PHP, only ASP).
But if you have it often (which it seems), then there is something else wrong, because I get it maybe once every 2-3-4 months or so - don't really know cause I rarely have cookies laying on my computer for so long
