For various Business Entities, you can import data to specific records you have created . For the Project entity only, you can view the downloaded data to check for errors provided that project workflows are enabled.
Any entries that show the Progress as ‘Complete with Errors’ will list those errors in the Result column. Click on the link there to view those errors. You can then edit the indicated rows on the file to correct the errors and repeat the dataload or can input data to the target entity directly.
Once all data is correct and complete, click 
then Delete to clear the entry.