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? 

Hi everyone,

As per the business requirement, customer should be able to attach up to 10MB of file while sending an email and it should get attached with the newly created case in Salesforce as an attachment. As per my knowledge currently salesforce file size limit for email attachments is 5MB per attachment up to 25MB total. I have been digging on internet but I could find at places that we can send an attachment of more than 5MB also.
If I want to attach a single file to an email, can you please confirm what max size it can be of?
Also, If we can't send a single file of size more than 5MB, what are the workarounds?
Thanks!