Can't write to Fat32 MicroSD disk
The SD Card is failing. Oddly enough, you can mount it as RW using a SDXC > USB adapter (don't ask my why, but it works) such as this. Once mounted, you can copy data off the card. It's not a question of a corrupted filesystem, but a physical failure of the device - for example, although you will be able to reformat the card when connected via this adapter, it will nevertheless revert back to read only if connected directly again; it will eventually fail completely. If citations are desired, I don't have any off-hand. My source is personal experience, multiple times over. Best of luck. 

Update (Found an old card):

Here is one of my old, dead 8GB SD cards that is read only when connected via my SDXC port:

...And R/W when connected via my USB. 


...And finally, immediately after I took these screenshots: