Strange dialog when trying to copy image files
I'm trying to copy a folder of duplicate images from my internal drive to an external drive to free up space. There are 36,000 image files in the original folder. Partway through the copy process I get a dialog popup that states The operation can’t be completed because you don’t have permission to access some of the items.
What causes this and how do I correct it? A "Get Info" on the original folder shows that I have read and write privileges, as does the receiving folder.
I'm familiar with Terminal commands but have no idea what to use to correct this.
Any advice would be greatly appreciated.
Thank you.
iMac 27″, macOS 12.3