Outlook 2011 and Exchange Configuration

I am having trouble getting an Outlook 2011 client connected to an Exchange 2010 server (SP3).  Here are the details.  When I do a send/receive I get the error “Unexpected data was encountered” and error number -17997.  

1)      I’m configuring the account using autodiscover
2)      In Outlook preferences the account ball is yellow (I’m not much of a Mac person but I think it’s supposed to be green)
3)      The Mac is on the Internet, not the LAN with the Exchange server
4)      Wintel machines can connect to the Exchange server from the Internet using Outlook Anywhwere and autodiscover with no problems
5)      When I run the account/domain through the Outlook Anywhere (RPC over HTTP) test on Microsoft’s Remove Connectivity Analyzer page (https://textconnectivity.microsoft.com), the account/domain passes with one warning.  It says “The certificate common name contoso.org doesn't match the mutual authentication string provided webmail.contoso.org; however, a match was found in the subject alternative name extension.”

I found several threads that suggest the problem is autodiscover.  They say the options are to 1) fix autodiscover on the server  side, or 2) turn off autodiscover on the Mac.  I don’t think 2 is an option for me as this mac has other Exchange autodiscover accounts and I fear changing this setting will break them.  I’m not sure what to fix on option 1 as the domain seems to pass Microsoft’s test with the warning.

Thanks for your help