If you're using Internet Explorer 8, there is a known problem with using the full message editor in our forum software. The problem shows up when entering longer messages, somewhere around 15 lines, you see the window jump back to the middle of the message rather than stay at the end. This makes entering a long message impossible.
There are 2 ways around this problem. If you want to use the full message editor, then set RVforum.net to run in compatibility view by going to the Tools menu and selecting Compatibility View when in the message editor. The easier work around is to use the Quick Reply message editor at the bottom of the each page of messages. This editor doesn't show the problem.
If you see this problem on multiple sites that you visit, then you can use the option on the Compatibility View Settings window to Display All Web Sites in Compatibility View.