I plan to offer a non-session option but it requires an extra table and some time to setup the routine to do it and I was in a hurry to get this plugin working as spammers here were 1 out of 4 registrations.
There are a few settings inside PHP that can affect sessions so it might be one of these quirks that affect it. What kind of configuration are you running on? Apache 1/2 ? PHP 4/5 ?
There is a chance I am setting up sessions incorrectly.
I use a views counter plugin here that also uses sessions so it might be helping me where without it my plugin fails, I'll test that.
(BTW spammers have now managed to get though my anti-spam image unfortunately
- I increased the difficulty but they still get through, though more slowly)