I have a situation where users recieve the following error when trying to view a library/list in Explorer Mode:
Your client does not support opening this list with Windows Explorer.
We have tried everything from the regedits, switching from Trusted Sites to Intranet, Hotfixes and restarting the webclient. We have experienced this issue in all combinations of Windows Vista, XP, IE 7, IE 8 and IE 9.
However, if the user installs SharePoint designer 2010 and connects to the site one time, windows explorer mode will work.
Windows 2008 R2
SharePoint 2010 SP1
Claims Based Authentication using ADFS as custom provider