I just ran into the same problem, and I will try to be as useful as possible. TLDR: you are missing a file in your preferences folder.
I created the problem by deleting things from my preferences folder (Macintosh HD/users/[my name]/library/preferences). I backed up the preferences folder before deleting because I intuited that some issue would definitely arise when I play with things I know nothing about, and then I deleted them all. Restarted the computer bc trash wouldn't empty. You and everyone else should not do this. Anyways, when I couldnt screenshot (same reason as you guys, no permission) I put the files back into my preferences folder from my hard drive and it worked again.
After extensive googling I found that the screencapture file should look like this:
~/Library/Preferences/com.apple.screencapture.plist
I still dont have that file, but my screen captures do work.
I know that all was super not-useful to almost everyone who is having this problem because who backs up their preferences? More importantly, who deletes their preferences? I had my reasons.
The (maybe?) useful bit:
I sorted the files in my preferences folder by "date added" (so as to see only the files that were added back in out of the 500 something), and there are 6 files that potentially fixed my screenshot issue. Now I know nothing about things generally, but I assume that the hidden ones called ".DS_Store" and ".GlobalPreferences.plist" don't count. Which means if you had the same screenshot issue, you are probably missing one of the other four.
The other four "new" files are:
- com.google.Keystone.Agent.plist
- com.apple.systempreferences.plist
- com.apple.finder.plist
- MobileMeAccounts.plist
Thats all I got. Don't ask me how my system functioned at all without the finder fie or the systempreferences file, thats way out of my scope. IDK if thats even the program file. Also, maybe the computer thinks the "date added" is the original date and none of these files matter at all. BUT I am positive that it was a preference that I was missing. I did nothing else to stop it from working, and once broken, no other steps were taken to make it work again.
Alternatively, http://www.maclife.com/article/columns/terminal_101_changing_screenshot_capture_ location