I have no idea what could be happening. If it happens to everyone then it would generally indicate a forum/server issue, but when it only happens to a few, it is very difficult to pinpoint and would generally indicate a user side issue. It may be that you have to clear out cookies, temporary Internet files/cache, and history. I'm using three different computers daily for now (switching out laptops on two of these) and I haven't had the first issue of the Shack not being found. I access many different areas of the Shack daily and am in and out over a dozen times a day.... so you would think it would happen with me every now and then...
Either way, you guys please keep us posted if it continues or if it clears up and what you did to clear it up... so we all know. We are open to any ideas.