Subnet column matching validation problems
This page shows any rows in the imported spreadsheet that contains errors. Any row containing an error will not be imported. You can go ahead and import only those rows that are valid, or hit Back to check the appropriate data is being imported.
If only a few rows have validation errors, you can export the errors as a spreadsheet. You can then import the valid rows, and then import the remaining IP addresses manually or as a new spreadsheet when corrected.
If all the rows in your spreadsheet have validation errors, check that the source and target columns match, and that similar column names have not been confused. Ensure [Do not import] is selected where appropriate.