The most common cause of the "Insufficient Data" error is either trying to use text X, Y, or Z values, or using a data file where the numbers are formatted as text instead of numeric values. To rectify this, you can:

1. Open the file in the Surfer worksheet.
2. Highlight the column of numeric data that is formatted as text (you can tell this if the numbers are left justified in the cells).
3. Click Data | Data | Text to Number.
4. Save the updated data file.