I figured it out. The problem was the firmware I downloaded one from another site. Then I put it on my SD card and it worked, thanks for the help anyways.
Rename the update to dstwoupdateb and boot the dstwo for 3 minutes then reboot. You should be goodHey I got a strange problem with my Supercard DSTWO I brought today. It was flashed and tested to be compatible with v 4.0.0-7E for the 3DS beforehand and it arrived I extracted all the necessarily files to my SD card and tried the SCDS2 out but it wasn't working on my 3DS saying "An error has occurred. Please turn the power off". I then used my micro SD card in my friends SCDS2 and it worked perfectly with my 3DS but not with my brand new one. Any ideas as how do I resolve this?
Sounds like they didn't flash the latest firmware, you'll need to obtain a non-3 DS and upgrade the firmware of the dstwo from that.
Edit: or you could try the method Fudge mentioned, but it's not recommended if you can get access to a DS.