I am getting this error while checking this challenge

i want to create a report with apex/vf but getting problem in how to calculations for total revenue , deals etc. Please help me as i am a beginner

Hi all,
I am looking for a mentor who can guide me development in salesforce. As i know Admin, Visualforce & Apex basics but i don't know to create a full fledged class. I am in a support project & want to move in development. Please help me !!!

I am trying to do the TrailHead Process builder Challenge"Automating Processes with the Lightning Process Builder". I have completed the Process and when I check the challenge I get the message below. I have tried elimanating the Country fields and changing to the Country Code field but I still get this error. Does anyone know what is going on with this challenge? 

  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: Update failed. First exception on row 0 with id 001o000000SFRX7AAP; first error: FIELD_INTEGRITY_EXCEPTION, There's a problem with this country, even though it may appear correct. Please select a country from the list of valid countries.: Shipping Country: [ShippingCountry]