500 Error - internal server error
A HTTP 500 Error (internal server error) indicates that something is misconfigured on the Exchange server, not within TouchDown. Please check with your IT department and have them check the event logs on the Microsoft Exchange Server to see what is happening.
Here are some links to additional information on this error:
http://technet.microsoft.com/en-us/library/dd439375(EXCHG.80).aspx
http://support.microsoft.com/kb/886346/
http://www.petri.co.il/problems_with_forms_based_authentication_and_ssl_in_activesync.htm
http://support.microsoft.com/Default.aspx?kbid=817379
http://support.microsoft.com/kb/330463