Don't know about the forums.
But I do know that in your hubs, all of your links will be marked nofollow if your Hubber Score is below a certain level. I think it's 70.
Your score at the moment is significantly below that, so you need to improve it. Write a few good hubs, participate on the site, and wait. It takes some time for your Hubber Score to improve.
As for technical reasons, I believe the "nofollow" is applied to your subdomain. Since the forum posts aren't on your subdomain, then there's no restriction applied. All of your hubs and answers, however, appear on your subdomain and thus get nofollowed.