Hi SnipeIt,
I am Dave, an Independent Advisor, I will help you with this.
Are you copying the files from iCloud online to your E drive, or from an iCloud folder your C drive to the E drive?
This error usually occurs when you select a large amount of data to be transferred and there is not enough space on the system drive (C) to create the required temporary data.
The solution that usually works is to copy the files in smaller groups, like 5GB or 10GB of data at a time.