When opening a Microsoft Office document from a SharePoint 2010 site in a rich client application (Microsoft Office 2007 or Microsoft Office 2010), I get one of the following results:
The document opens slowly.
I am prompted to enter my credentials multiple times.
Opening any other - non-Microsoft Office - document (like PDF files) is fast.
I see multiple authentication failures for the http://<sitename>/_vti_bin/shtml.dll/_vti_rpc URL in a network or Fiddler trace.
SharePoint Web Front End (WFE) server(s) has Antivirus software installed and the exceptions are not set correctly.
Removing the antivirus software or setting the correct permissions for the antivirus software resolves the issue.
Proxy settings in Internet Explorer is set to automatically detect proxy settings.
In Internet Explorer go to Tools->Internet Options->Connections->LAN Settings and uncheck Automatically detect settings.
This can also be done through group policy by going to User Configuration->Policies->Windows Settings->Internet Explorer Maintenance->Connection->Automatic Browser Configuration and uncheck Automatically detect settings.