Using GBA Backup Tool or an alternative?

I'm trying to get a backup of my save from a commercial GBA game (ROM 0015). I've had the game coming up for 11 years and am a little worried that I don't have a backup of my save.

I've tried using GBA Backup Tool 0.1, 0.2 and 0.21 but it won't let me create a copy of my save, the option is greyed out. I have tried it with a copy of Max Payne which worked fine, but no luck with Fire Pro Wrestling.

I'm using a DS Lite, EZ-Flash Vi and also have access to a Supercard SD Micro Lite.

Does anyone know what I'm doing wrong? Is there a way around this or can anyone suggest an alternative method of taking a backup without buying extra hardware?

I have tried Googling answers but I haven't found any other solutions.

Thank you :)