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&...
Apache warning: Not Acceptable An appropriate representation of the requested resource / could not be found on this server.
Apache/1.3.34 Server at webmail.****.com Port 80