Okay, this may have already been addressed, but just in case it hasn't... or if someone needs a quick reference....
If screen shot (from press/hold power) is not working for you....
Then you can manually change the permissions of the required file to get it up and running.
Navigate to system/bin/screenshot file. Choose permission settings. Set file permission to 7777 (full access). Though you may not need full access, it should not hurt anything... as long as you don't go in there and f**k with anything

.
I personally use jrummy root browser to navigate through files... but you may use whicheever file browser you wish.
You should have no more bitmap/null error
Seeeeeeeeya!