Just starting today (for no apparent reason), I get the error below when I either go to this page:
http://www.discoveryplayground.com/curriculum/...

or when I try to add any block or modify any stack:


Warning: require_once(/home/therap3/public_html/discoveryplayground/updates/concrete5.6.0.2/concrete/models/json.php) [function.require-once]: failed to open stream: No such file or directory in /home/therap3/public_html/discoveryplayground/updates/concrete5.6.0.2/concrete/core/libraries/loader.php on line 40

Fatal error: require_once() [function.require]: Failed opening required '/home/therap3/public_html/discoveryplayground/updates/concrete5.6.0.2/concrete/models/json.php' (include_path='/home/therap3/public_html/discoveryplayground/libraries/3rdparty:/home/therap3/public_html/discoveryplayground/updates/concrete5.6.0.2/concrete/libraries/3rdparty:.:/usr/lib/php:/usr/local/lib/php') in /home/therap3/public_html/discoveryplayground/updates/concrete5.6.0.2/concrete/core/libraries/loader.php on line 40


I have cleared the cache and did the "refresh database" from the dashboard and it didn't help.

Any suggestions to what caused this and how to fix it?