When trying to create an e-mail from OWA the following error message appears:
'Your message body is too large. OWA only supports message bodies up to 100K...'
This message appears even when there is only one line of text with no attachments.
We usually see that message when the user is replying to or forwarding a long message. The error message, as you may have surmised, is actually incorrect. The limit on replies and forwards in OWA is much closer to 30K than 100K.
The only solution (until Exchange 2000) is to break your message into smaller parts or trim the message that you're replying to or forwarding.