I cannot complete the "Create custom objects and custom fields" Challenge. I am getting this error message: 
Challenge Not yet complete... here's what's wrong: 
All the expected custom fields for the Trail__c object could not be found.

Although I am pretty sure I got the right:

What am I missing?

The following formula is shoing an error. 
DATE( 
YEAR(CurrentEndDate__c + GracePeriod__c ),
(MONTH(CurrentEndDate__c + GracePeriod__c)+1), 
(1) 
)-1

CurrentEndDate__c = 11/30/2015
GracePeriod__c = 30

Please help!