Im using windows, and yes, camera does not show "card locked" warning.
If the camera does not show card locked, and CHDK is not loaded, then the camera isn't detecting the lock. In this case it won't even try to load CHDK.
The lock detection is a physical switch inside the camera, which is actuated by the plastic tab on the card. The card side of this has no electronics, it's just a lump of plastic you can move around.
The lock switch can get stuck, or a marginal switch or card can fail to engage. Some cases of stuck switches have been reported on this forum, and resolved by poking the switch. It is also possible that the electrical connection to the switch is bad, but I'd guess this is less likely than mechanical problems.