I'm currently on Catalina 10.15.4 and recently started seeing a popup whenever I try to take full screen screenshots. A window pops up saying "Your screenshot can't be saved. Unable to capture window image." I've tried to capture via the grab tool and also pressing ⌘ Command ⇧ Shift 4 then Space then and then clicking.
I've tried changing the default directory that my screenshots are saved to from the desktop to a folder called screenshots but this didn't help.
defaults write com.apple.screencapture location ~/Screnshots.
Any ideas why this might be happening?