The software thinks there was a CSRF error. The fact that you are seeing this means there was not in fact such an attack. There are three main reasons you might see this page:
You've had this browser open a long time and tried to update something without loading another page in the interim. For example, you were on the form to create a new post, went for lunch, had your session expire and came back. To resolve this, go back and reload the page. This will give you a new token and you'll be all set. If you find this happening to you a lot, post exactly what you were doing in the forums and we will see if we can do anything to help you out.
If you were just trying to view a page and not update something, we have a bug at our end. For example, maybe you clicked the search link and saw this screen. If you think there is a bug, post the date/time/timezone and what you were doing in the forums.
If any of these apply to you, try to post to let us know about it. If the error prevents you from posting, email what you were trying to do and which of the three categories you think the error falls into to bookpromotion at javaranch dot com and moosesaloon at javaranch dot com