My experience with the plugin is a bit little different.
I had so many errors with the plugin like many of you. Both WP and bbPress would never sync with plugin settings like secret key and etc. Well, maybe once in 100 refreshes, but once I enable both side, it would just fail soon after.
Turns out, it was the server settings. DNS to be more precise. The fix? I'll get to that later.
This plugin is very strict with connection between the both WP and bbPress. Usually they're placed in the same server, or so you would think but that's not 100% true. And since every server settings are different, we might get many connection problems. Some servers will see the plugin as a port attack. Some servers won't even allow the connection between both side of plugins for security reason. So far, some of the problems here could have been fixed with editing the source codes, but I usually don't like to do so because when you upgrade the code later, it can easily break the code.
Anyways, in my case, it was the DNS and NS problem that was causing the sync problem between WP and bbPress side.
Servers and internet nowadays are smart enough to automatically point to the right server, even without the textbook-correct DNS zone settings. If you think you've setup the DNS correctly, and pointed to the right NS, and still can't get both side to sync, I suggest you to try this first:
http://www.intodns.com/
Visit and type in your domain name and see what results you are getting. For the 'Parent' and 'NS' section, you shouldn't have any yellow-colored warning signs. Maybe couple like 'Different subnets' and 'Different autonomous systems' but nothing more than two blue "i" icons and green check marks for rest of them. With this tool, me and my webhosting server admins spotted the problems and worked together to fix many DNS settings. I still can't believe that people could connect to my website even with the crappy DNS settings. Well, it was me that did the poor job but I'm new to VPS and still learning, so...
After fixing the DNS zone problems and pointing to the right NS, the plugin works like a charm. And my website actually connects faster from all over the world. Ping time is better too and as much as I hated the plugin, it was totally worth the time and effort.