Hi Matt,
Whilst I can't say I have experienced this, and all other things being equal, I'm guessing you are using AAM and different URLS for internal and external access. I would suggest trying initially to recreate your AAM definitions, or failing that if you have extended the web app for the external site, removing Sharepont from that website / virtual server and extending it again.
Iain
Iain Wyatt
BEng, MCTS - Moss 2007: Configuration & WSS 3.0: Configuration
Novotronix