First check the physical lock switch on the side of the SD card. If it has moved to the lock position, the computer will treat the card as write-protected.

If the switch is not locked, the issue may be with the computer, card reader, or the card’s read-only attributes. On Windows, one community fix is to use DiskPart to clear the read-only flag on the card. Some users also mention checking the Windows registry storage-policy setting.

That said, this is not typically something a Nikon D5200 should repeatedly cause by itself. If the problem comes back after reinserting the card, common suspects are:

• the SD card’s lock tab slipping
• a faulty card reader
• the card itself developing problems

Safest approach:

1. Back up your photos.
2. Check the SD card lock tab.
3. Try a different card reader or computer.
4. If needed, clear the read-only attribute in Windows.
5. If it keeps happening, replace the SD card.

Avoid forcing writes to a card that may be failing, since write protection can sometimes appear when media is going bad.