It could be... a similar issue was reported earlier. Make sure all links into your forum are the same as what your forum lists as the url to the forum. (ie: if your forum includes the "www." in the url your links into the forum from your front page need to include it too).
I had the same problem but after all the members help like yourself it is all corrected as it was just the same url issues as you explained. Now all my members and myself can see the shout box correctly.
since upgrading to 7.3.1 both myself and users have been reporting that contents of shoutbox are "disappearing". this is for all browsers. it only happens intermittently.
refreshing screen and deleting cookies etc etc does nothing. the problem is fixed, however, by going into preferences and pressing submit. shoutbix contents then reappear.
JakChat.com -- Forums for Indonesia's English-speaking community Ubuntu-Indonesia.com -- Forums for Indonesia's Ubuntu Users
in addition to above, it appears guest users cannot see contents of shoutbox until they register. registration means, of course, saving preferences at some point.
i can only speculate that there is a stray variable somewhere not being initialised.
JakChat.com -- Forums for Indonesia's English-speaking community Ubuntu-Indonesia.com -- Forums for Indonesia's Ubuntu Users