What browser are you using? Keep in mind that the site was designed to work best with Internet Explorer or Netscape so other browsers may not function as expected.
When you click on the Preview Post button the preview should pop open a new window for you to view the post. The window where you were entering the text of your post should still be open and available for you to hop back to in order to make any corrections/additions/or whatever.
Here's a tip for working on a longer post message. Open a NotePad or WordPad window and type the bulk of your text in there. When you're ready to preview or post the message copy the text from the NotePad/WordPad session and paste it in the Post Reply box. Do any tweaking to the message (like bolding, changing text colors, inserting Smilies, etc) and then preview or post the message. That way if your text is lost for some reason you still have the bulk of it available in the NotePad/WordPad session.
Hope this helps!
The site logs you out have 20 minutes of inactivity or being "idle".
So if you are typing in a reply that takes you 30 minutes, during that time you are on the same page (not moving between pages) so the site thinks you have gone away and logs you out. So when you go to post, it has to log you in again and forgets what you wrote in the post window.
Norsky's ideas above are helpful, but anothing thing you can try...
If you know as you are writing a post that it is taking you a long time, (say more than 5 minutes) click the "Preview Post" button even if you aren't finished. That way, the site will see you are still active and reset the timer again for 20 minutes from the point that you clicked "Preview Post".
-Adam Wartell
NCM Lifetime Member #1222
Founder: C3 Vette Registry
C4 Vette Registry, C6 Vette Registry
My first Vette, now owned by JB79: