FastCopy worked for me. If anyone else has this problem, download FastCopy. Go to Options and set it to Diff HDD Mode. Then in the drop down menu select Diff (no overwrite). Then, execute.

I had not considered using a separate program. I'll give it a try. Thanks!

I have a 3TB external hard drive that I use to backup large files. Usually, I just drag and drop the folders from my laptop to the external drive and Windows gives me an option to skip duplicate...