Trying to complete "Community Rollout Strategy" and Create Sharing Rules Unit. Everytime I click on "Check Challenge", I get this error: 

Challenge Not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.QueryException: List has no rows for assignment to SObject

Any advice? Or do I have to start a new DE org? 

Hello all, I am insure where to access this sharing set mapping , could someone point me in the right direction please?
Thanks,
Seth

 

 Everytime I try to save a visualforce page in the setup section I get the following error:Error: <apex:page> is required and must be the outermost tag in the markup at line 1 column 1

I get the error if i edit the page, if i try to rename the file or even if i open it up and just hit save. This is happening on all visualforce pages. Any ideas? My Code: (This is just the standard SFDC Login Visualforce page.