That message is triggered by the small lock tab on the SD card and the camera’s card-slot lock sensor. If the card works in another camera, the issue is likely one of these:

• The card’s lock tab is loose or not staying fully in the unlock position.
• The 70D’s card-slot sensor may be bent, stuck, or damaged.
• The card may not be fully seated.

Try these steps:

1. Reinsert the card carefully and make sure it clicks fully into place.
2. Test with a different SD card that is definitely unlocked.
3. Inspect the original card’s lock tab for looseness or damage.
4. Look into the card slot for debris or a bent sensing tab.

If multiple unlocked cards give the same warning in the 70D, the camera’s card-slot write-protect detector likely needs service. Avoid forcing anything into the slot.