First, this has been intermittent, but affecting all users.
Exch 2003 sp1, Win2003.
Accessing OWA from anywhere (LAN or WAN) produces the authentication box, followed by "loading" ending with outlines of blue square boxes on top and to the left of the screen.
It says loading, but then dies, with "error on page" on the status bar.
I've checked the authentication rights, patched with the pre SP1 Win2003 hotfix, etc.