This works fine for one partner but the other one cannot upload multiple documents using Explorer View, they recieve the following error: "Your client does not support opening this list with Windows Explorer"
Sharepoint is accessed over SSL using IE8. I have verified the following on the client that isn't working:
* The site URL is added to the Trusted Sites zone in Internet Explorer
* IE is not running in 64-bit mode
* The WebClient service is started
What further troubleshooting steps are available?