GroupWise 2012 login prompts user to download "webacc.exe" file

After upgrading GroupWise WebAccess from version 8.x to 2012, when users login, instead of seeing their mailbox, they see a blank page and are prompted to download a file named "webacc.exe"

 

The problem happens because in some circumstances the 2012 WebAccess upgrade process does not correctly update the "Handler Mappings" settings for Internet Information Server.

To correct the problem:
1 - Start IIS Manager on the problem Windows 2008 server
2 - Highlight the web server object (not the "default web site" object)
3 - Click on "Handler Mappings"
4 - If you see two entries for ISAPI-dll, highlight each entry (one at a time) and click "Edit" to view the properties, and then delete the entry that points to the old location for the GroupWise 8 redirector at: C:\Novell\GroupWise\connector\bin\isapi_redirect.dll
5 - If you see only one entry for ISAPI-dll, highlight that object and click "Edit" and then change the path to the correct location for GroupWise 2012 at c:\Novell\connector\bin\isapi_redirect.dll
6 - After making the changes, stop and restart the Worldwide Web Publishing service, and users should then be able to login to GroupWise 2012 WebAccess.