That’s because you are trying to open a CSV file but it contains lines where the number of columns is different from other lines. You can double-click on the message:
filename (number): Inconsistent number of columns detected.
and jump to the number’s line of the “filename” file, and correct the line by adding or remove a separator (usually comma).
If this is not a CSV file, you can simply ignore the message, and either (1) disable CSV detection by going to Configuration Properties – File tab and clear all the CSV files to Detect check boxes, or (2) Customize dialog – CSV tab and clear the “Validate CSV and Output Errors” check box.