Screenshot area to clipboard (Control + Command + Shift + 4) doesn't work According to the Mac support docs, I should be able to use Command-Shift-Control-4 to take an area screenshot to the clipboard.  

This doesn't work.  What am I doing wrong?  Whether I use an external keyboard or not it doesn't work.  

Command-Shift-4 works just fine.  I'm on 10.11.6
Things to check...


The receiving app can accept the format, .png by default.  
The buffer hasn't been replaced with other content, text etc.  
If  Cmd ⌘   Ctrl ⌃   Shift ⇧   3  would work to capture the entire screen to clipboard.  
That the key commands are on &amp; set to defaults in System Prefs > Keyboard > Shortcuts > Screen Shots &amp; also that resetting to defaults doesn't generate an orange warning triangle that another shortcut is using the same key command.