I'm trying to back up my pictures
You don't mention exactly, what software or method you are using for this task, but.....
Based on the thread title it sounds like you are trying to copy them from one location to another.
IF you go to C:\Users\YourUserName\Documents and with that container open and using your keyboard strike Ctrl + A (that should select all ) and then Ctrl + C (that should copy "all" to clipboard)
Do you get an error message right away
OR
Does the error message occur when you try to paste them to your archive location.
Try creating a new folders, call it Docs_Bkups, open that up and then use Ctrl + V to paste everything from the clipboard to the new folder