The HTTP 500 Internal server error is a generic error message which Internet Explorer uses to "hide" an actual ASP script error. To see a meaningful ASP script error, go to Tools/Internet Options..., open the Advanced tab, and under Browsing, uncheck the option Show friendly HTTP error messages. Then attempt to connect to the SAWeb again. Also check to see if you are getting any errors in the Unity server's Application event log or System event log when you get the error. This Cisco doc is a good place to start as well - http://www.cisco.com/en/US/customer/products/sw/voicesw/ps2237/products_tech_note09186a00801ba0ef.shtml
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.