Why do I have to log on every so often?
Why do I get a visual validation screen when posting a message
Why does my name say GUEST
 

Its because you are not logged in. This has everything to do with cookies. For some reason you became logged out and you are now trying to post a message as a guest. That requires a little extra validation to insure we get less spam messages.
 
Usually when you log in your information is held in a cookie on your own computer. Each time you come back to this site it reads that cookie and knows who you are. Did you delete cookies lately? If so, then each time you do that you should expect to have to re-log onto all places you normally visit. Not just this one.
 
When deleting cookies, be sure you know which ones you're deleting.