On a Mac, MacOS 10.13.3, it seems you have to format the SD card with:
* MBR partition scheme
* FAT32
I got the following to work (assuming your SD-card has "disk2", you might have to do this in your terminal.
#make sure that your SD card really is disk2
diskutil list
#If you are convinced that your sd card really is disk2
sudo diskutil eraseDisk FAT32 3D MBRFormat /dev/disk2
If you do not specify that your SD card should be partitioned using MBR partitioning scheme, MacOs will format it using GUID scheme, which the printer cannot read. I have formatted 16GB cards this way, and they can be read by the Ultimaker 2+. Id does not seem like there is an easy way to do this in the Disk Utility anymore.
//magnus
