Sometimes there is a delay after you make 20 posts as the system catches up. Some people have trouble with the price; I believe you have to be sure not to put cents in. You might be able to solve it by clearing your cache.
If you can't figure it out, tell us the steps you are taking, if there is an error message, and if possible give us a screenshot of where things go wrong. Also, tell us your OS and browser.
If you can't figure it out, tell us the steps you are taking, if there is an error message, and if possible give us a screenshot of where things go wrong. Also, tell us your OS and browser.