Can you please confirm that you are using the latest version (1.0.7).
Please also ensure you are scrolling down to the very bottom of the Storms grid when looking for the custom events as they may be at the end of the list. You do not need to select any of the event checkboxes when using custom events as they operate independently.
If this does not work, perhap you could send through the ESI file saved after you try to Generate Storms.
Regards,
Chris