Thanks for the data. It helped. Here is what I did:
1. Created a new project and added Port VilaBoundary.shp to the map.
2. Checked the layer's Properties and saw the projection and the Extent as shown below. Notice that all extent values are positive numbers. Which match the "N" (north) coordinates displayed at the bottom of the map (by the red arrow). I am not sure why the y coordinate at the bottom of your map shows "S".
3. I used "Browse..." option to browse to and select Port VilaBoundary.shp. The Template Extent values other necessary coordinate values were populated automatically. Specified 70 and 70 as the Cell Size Width and Height, and Polygon as the Geometry Type. The tool ran successfully and the fishnet was created as shown below.
Could you try the above and see if you get the same fishnet?