I think I know what this may be - and it is probably a caching problem
I removed one of the advertising banners so the rotation link now only displays 4 rather than 5 images.
To do this I simply changed the script from 4 to 3 (the google one slots in differently) and then removed the image from the server.
What I imagine is happening is that your browser will have a cache of the old script which calls rotation 1,2,3,4,google... only now it cant find image 4 so thats possibly when you see the message.
Can you let me know please if it continues... because Ive just thought of somewhere else where it may be being cached.
Such as those ISPs that use a proxy server like AOL (and if TT are using AOL's proxy).