Check that this item does have a check mark. If the box is blank, put a check in it.
Control Panel > Primary Settings > Disable HTTP Referer Check?
Unselecting this item may cause login and posting issues for your members. We recommend keeping this box checked unless you have a special need for this feature.
Also while you're at that same page, check your "Custom Cookie Prefix". If you personally are having the problem, remove anything from that box and try it again. Then if the problem goes away, you've found the cause. If the problem still persists, put back the value that you just removed from that box. Confirm that no spaces are being used.
And lastly, review the item at the very bottom of that page:
Cookie Expiration Time In Seconds
86400 = 24hrs
604800 = 7 days
2592000 = 30 days (Recommended)
