Error Copying SharePoint Files in Windows Explorer

I was trying to copy files from a site on one SharePoint server farm to a site on a SharePoint server farm outside the firewall. The source site was using HTTP and the destination was HTTPS. I opened both document libraries in Windows Explorer and copied/pasted the files to the destination. The copy would create the folders but throw an error on every file, “an error occurred copying some or all of your files”. 

I noticed I had IE 6 installed so I installed IE 8 and everything now works perfectly…