I got this issue with a brand new 32GB SanDisk Ultra microSD Class 10 when trying to copy data with my laptop:
"The disk is write-protected"
It took me about 20 minutes to find out why.
I could save images to the the microSD when inserting it directly to my smartphone (without the microSD adapter.
The root cause: The lock switch on the adapter is loose, it may slide to Lock position when I insert it to my laptop's SD slot.
Hope this sharing can save you time!