Well, you can check out the FAQ posts child forum for general troubleshooting.
First, I would run the test to see if your ds has the older firmware or newer firmware. Only the older ds firmware is directly compatible with the magic key.
Then, I would make sure I was using gst-patcher 3.1 on your roms before flashing them to your cart (gst-patcher 3.1 doesn't include the latest roms, though, so you're going to be limited in that regard)
BruceG