I'm getting an error when running the exploit.
Try clearing your cache and cookies in the 3DS Internet browser (deleting save data also may work). This appears to be a known issue and this is the current workaround. Also, try removing any gamecards in your 3DS and don't press any buttons until the top screen has turned grey, from here you can press L to bring up the Gateway menu if you have run the exploit before or the R button to update the Gateway 3DS card. In addition to these, ensure that your SD card is formatted to FAT32, as some other file partitions appear to be causing problems (e.g. NTFS, exFAT).