Posts in Selling Forum are free.
I do not know why you cannot post there. In the past there were restrictions on new members. These were removed and I am not aware they have been reimposed, although there have been some recent changes to software which may have had an effect.
You will need to wait until Erin comes along to see if he has an answer.
In the meantime you might try logging out, clearing cookies then logging back in (gives the sense of doing something).
Please don't post about your books in the other forums.