Sorry Crispy, are you saying about my forum or oficial DNN site (here)? Cause I just try now in my site and in my user´s (3 accounts, host and 1 admin and 1 normal user) settings there is no subscribed forum, I even subscribed all founs and out, didn´t work, I tryed with all my accounts.

Also the trust user setting in forum user settings is locked (gray), I can´t change, all user´s behave like this. My ideas for now is over.

                       < when I click edit forum, it goes error >

I was getting the same errors but on all of my forums. Logged in using a different account and was able to start a new thread with no problems. Did some hunting around and I figured out the cause! I had originally selected the "Email me" option at the bottom of one particular thread. A few days later is when I started getting these error messages even though I had posted in other threads after I had selected that option (why it took so long to start showing the errors is beyond me). I noticed that when I went into the Tracking/Subscription section my user settings, that none of the forums/subforums were selected. As soon as I selected the forum where that thread resided and updated my settings, I was able to post/start new threads again!

The bad part was that when I had gone back to the thread  I originally had selected for email notification, there was no way for me to tell that I had that option selected. That option looked exactly like it did before I had selected it. I checked this before I changed my user settings. I tried selecting the option again to see if I could clear it out, but received an error about trying to add a duplicate key (unfortunately I didn't write down the exact error message). While trying to duplicate this, I unselected the subscription to the forum and tried to reselect the "Email me" option. Tried posting a new thread and was able to duplicate the Add/Edit Post is unavailable message. This time, the email me option was showing as checked. As soon as I unchecked it, the page refreshed with no errors then I was able to post again. So in summary, it seems like there's a bit of a glitch with how that Email Me option shows the first time you go to use it especially if you don't have your general forums subscriptions selected.

I hope this helps folks!