Now we are in the new structure, there's a hidden forum called "Misplaced Posts". This is where posts end up if you try and add one to a forum that is set to be read/only. So, how does this happen?
You can click on a top level forum name (for example "Image Discussions") and you will see something like this:
Note the two areas I have circled. The first one says "subdirectories". The fact that there are subdirectories is an indication that you MAY be in a read only area. But not always. The second circled button shows you CAN start a thread from here. But note that if you do, you will get this screen:
Look where I've circled. It says "Misplaced posts". This is an indication that you can't post where you though you should. If you click on the little down arrow next to that text, it comes up with a list of forums you CAN post to - and you will see the ones you can't as slightly greyed out. So, choose the correct forum here and all will be well. See picture below:
I will be checking the Misplaced Posts and moving them out of there if I know where to put them. Otherwise, I will contact you via PM and ask. If you see it in the wrong place, message me and I will fix it.
Alan