SD card slot is always read-only I have a 4 GB Micro SDHC card and I use a Micro SD adapter sleeve to read it with the built-in SD card slot of my 15" mid-2010 MacBook Pro. It's been a while since I tried to use it, but I just realized that my Mac will always treat it as read-only, no matter the position of the physical lock on the adapter sleeve.

I can't even format the partition because all the options in the "Erase" and "Partition" tabs of Disk Utility are grayed out for the SD card.

Why is the card read-only, and more importantly, how can I write to it?
In my case, a physical misalignment is causing the read only status. Gently pushing the disk away from the display reliably makes my cards write again.