It looks like to me that you, perhaps, have your server setting incorrect in Dreamweaver. Because looking at the error, it references two completely different paths.
Notice that when it tries to open the session file it starts with this: /home/users/web/b2295/
But, it appears its looking for the file using the directory that starts like this: /hermes/bosweb/web229/b2295/
I think is what your seeing is that it is trying to pull from an incorrect location - which is trypically a server setting issue when you setup your site definitions in Dreamweaver.
As a guy who has used Form Builder a great deal, I can confirm that it works as advertised. I will be around all weekend to offer any more assistance if you want to troubleshoot some more. A couple of things you might want to do though, is post a link to where the users on here can see it in action, as well as, post the code from the page here.