i am getting the following error again and again.i have made custom object with label "Trail" and API name "Trail_c" with 3 custom fields.
1)field label-Description       API name-Description_c
2)field label-Distance           API name-Distance_c
3)field label-Last Inspection Date                    API name-Last_Inspection_Date_c
all data types are also fine.i can't figure out what's the problem
"Challenge Not yet complete... here's what's wrong: 
All the expected custom fields for the Trail__c object could not be found"
 

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.DmlException: Insert failed. First exception on row 0; first error: FIELD_INTEGRITY_EXCEPTION, User: id value of incorrect type: 00536000002OPa4AAG: [User__c]

I saw a post reply saying to delete USER and recreate the field but I am unsure if I am supposed to create a new OBJECT under Campsite Reservation (directions say "Add a custom field...")

This challenge has given me fits for two days.  This is my latest error message I managed to fix the two previous...  THANKS.