My phone's micro SD card suddenly became read only recently. Despite I bought the card for about 6 months at that point, the googling results suggests that my card has "died".
The symptoms are as follows:
- Photos can be taken but the pictures are not saved (maybe due to the phone caching data and so only fails when it writes the cache).
- Messenger apps takes a longer time to load (maybe due to messages after the SD card becoming read only are "new" messages that needs to be retrieved).
I also took the card out, put it in an adapter, and try writing files to it on my PC. The interesting thing is that this seems to work. I can see the file being saved, and I can open the saved file. However, the new file disappears after I rejecting the SD card and then reinserting it back to the PC. I also try formatting the card on the PC. It seems to work for a little while and then fails at the end. I assume in both cases it is due to data caching.
From googling around, it seems SD cards simply becomes read only when it dies. It's like a big piece of paper that you can cross out what you have written but not erase. So eventually, there's no more space to write anything new. Here is a Reddit post that talks about the issue.
https://www.reddit.com/r/techsupport/comments/239ctc/micro_sd_card_has_suddenly_become_readonly/
A lot of "solutions" suggests that you make sure the read-only tab of your SD card isn't set. If you are checking the card on your PC using an SD adapter, do check that. But, if your SD card really did "died" and become read only, the only solution is to get a new card.
If you, like me, have a Lumia phone and the SD card are loaded with your apps, it will take a while to "move" your data from the old card to the new card. Initially, I tried copying all the files from the read only card to the new card. But the Lumia phone seem to know that the cards are different and so it won't use the data and app files I have copied to the new card. Instead, I have to follow the following forum post's suggestion -- that you can moving apps from the read-only SD card to the phone using the phone's move function, and then move the same data from the phone to the new SD card works. It is a very slow and annoying process. See the post of "mohit jaisingh" for details.
http://forums.windowscentral.com/windows-phone-8-1-preview-developers/291466-move-app-one-sd-card-another.html