Opus's Create Folder dialog allows you to specify a full path, and you're pasting a full path into it.
If you don't want the full path, you need to remove everything except the name or sub-path that you want to create.
If you want a button/hotkey which copies the current folder's name (rather than full path) to the clipboard:
@nofilenamequoting
Clipboard SET {sourcepath|nopath|noterm}