I think I might have it, then. One issue with cookies that pops up every so often has to do with the "www". If you use
http://www.tickletheater.com to access the forum, a cookie is made for
http://www.tickletheater.com. However, if you type in only
http://tickletheater.com, the cookie for the address with www will not work and you will have to log in again. Then, whenever you click on a link inside the forum, you are taken to a page using the "www," as the forum software appears to be set to produce links with www included. Do you normally just go to
http://tickletheater.com when you visit the forum? If so, try with the www and see what happens (Type in
http://www.tickletheater.com, log in, and browse. Then close your browser as normal and restart it. Navigate back to
http://www.tickletheater.com and see if remained logged in you do.).
EDIT: The more I think about it, the less I like that answer. I'll wait and see what you or Cynthia has to say, however, before I think of more possibilities.