Hi,I am preparing for my SF Admin exam.Chanllenge is to  Import Data using Data Import wizard..
Before importing I cleaned the .csv file removing all the - from phone numbers.Merging first name and last name into a single Column called NAME. Also mapped CELL TO MOBLE.Then import the data which was successfully completed but then I got "Challenge Not yet complete... here's what's wrong: 
All the contact records from the CSV file were not found in the Org.".What does that mean?

Hi, 

I'm new to Salesforce and doing the beginner's admin Data Management Challenge. It keeps giving me an error message saying, 
Challenge Not yet complete... here's what's wrong: One of the contact records from the CSV file could not be found in the Org.​

Even though I've already uploaded the sample import data on my Dev Org without problems.

Any advice on this? Thank you!