Why does this happen?
 

A member logs in and gets the "thank you for logging in *******."
then it goes right back to the sign in page again.

Any ideas why?
It doesn't happen to all members just s few.:confused:

I sometimes get this I think it is a cookie error, if they scroll down to the bottom where it says "Active Users" they see themselves online if they click their name they become logged in.

I usually just clear my cache and it works.

You may have your cookie path set incorrectly. Are users able to go to your site via both yoursite.com and www.yoursite.com? You may want to redirect one to the other and then make sure all your site urls are consistent.

Yes both ways work.
A few members are still having the problem as i said in the OP.
What and where should i set the cookie path Lynne?

:confused:

Google 'htaccess' and you can find out how to use htaccess to direct all your www.site.com urls to site.com or vice versa. Or, you can set the cookie path to .site.com (with the dot in front of the name). I like the htaccess way better.