I tried to install the fast and secure contact form plug-in and experienced an error message after entering the captcha code. Said that it could not set the cookie’s. I found this page on the subject regarding the same error in a comment captcha plug-in by the same author.
Oddly, I was able to send one message from the form when I switched themes back to the classic theme, added one comment to a random post. But then when I switched back to the custom theme, I got the same error message.
This is vaguely similar to the problem that CoffeeCup HTML editor has in uploading a file to a new folder. It cannot write to the new folder until at least one file has been created there. After the first file is created, it uploads fine.
In any event, I could not get it to work, so I uninstalled it.