I found a remedy for the situation at hand if you have access to your database. 

Go into your database and navigate to the dbo.Forum_TrackedThreads table.  In there you will see results that show

ForumID, ThreadID, UserID, CreatedDate and ModuleID

you will notice the UserID of the account not able to post in there. In my database there were 4 records, three of which I am sure were not able to post and am awaiting the forth user to log in and test the theory before i delete them.  The three users of the records I deleted are all able to post now.

Just delete that row, and voila, you can post again.

I know this is just a temporary work around, but will get you back up and posting faster than any other method mentioned. 

I have the same problem in my forum.

Every help is apreciate.

Thanks

I've been unable to post on these forums for the last 2 months, but today it was urgent, so I had to set up a new user account (meet RodneyJoyce1) - obviously this is not ideal - I wonder how many user accounts have been duplicated... I also have the same problem on my Smart-Thinker forums - I am not sure it's being taken too seriously, but I consider it a critical problem.