Ok, I'm still getting this error.
This is happening when I forward a message. Its only happening on particular messages though. Seems to be a problem with how RC is handling the headers.
URL:
http://webmail.****.com/?_auth=805d974c62b6acfd5d353f5e3756a251f174ae60&_task=mail&_action=compose&_forward_uid=1510&_mbox=INBOX
Apache warning: