Your Camera Says "Card Error" or "Cannot Access Card"

This walks through the write-protect switch, when to format in the camera versus running the SD Association's own tool, and how to tell a card that just needs a clean format from one that needs to be replaced.

The short answer

Three different problems can produce the same message. Work through them in this order: the card's physical write-protect switch, if it has one; a plain in-camera format; and only then, replacing the card. Format in the camera the card is actually going to be used in, not on a computer, unless you have a specific reason to reach for the SD Association's own SD Memory Card Formatter instead of your computer's built-in tool. If a card that is correctly unlocked throws the identical error again immediately after a clean in-camera format, that points to the card, not the format process, and no amount of reformatting will fix it.

Check the write-protect switch first

Full-size SD, SDHC and SDXC cards carry a small sliding tab along one edge of the card body. Canon's own support documentation describes what happens when it is down, in the locked position: the camera cannot write or delete, and it tells you so on screen, naming the write-protect switch directly. The fix is mechanical, not a format — slide the tab up, toward the metal contacts, and try again. This produces a card error on a completely healthy card, which is why it's worth checking before you touch the format menu at all.

Format in the camera, not on your computer

Once the switch is ruled out, the SD Association is specific about its own tool: it recommends the SD Memory Card Formatter over the format tool built into Windows or macOS. Its stated reasoning is that general-purpose operating system formatting is not optimized for SD-family cards and can cost you performance. The SD Association states that its formatter is built to comply with the SD File System Specification. None of the camera manuals cited on this page make that same claim for their own in-camera format function — but each one documents its own formatting steps as the standard way to prepare a card for that specific body, which is the simpler default when the camera is already in your hands.

What the format step actually looks like on your specific camera varies more than you'd expect. Three current examples, each checked against the manufacturer's own manual:

Nikon's own documentation notes that this procedure changed between firmware versions on the same body — the full-format steps for CFexpress cards on the Z6III were revised after launch. That's the practical case for checking your own equipment directly: open your exact camera's current online manual, search "format," and read the page for your model and current firmware, rather than relying on memory of how a different body, or an older firmware version, behaved.

What formatting fixes, and what it doesn't

Formatting rewrites the card's file system — the index the camera and computer use to find files — not the physical memory cells underneath it. The SD Association describes its formatter as clearing up problems like a card that wasn't safely ejected, or performance that has degraded over time. That's a logical-level fix. It is not a repair for flash memory that is physically wearing out or a card controller that's failing, and it will not get your files back afterward: every source here that addresses formatting treats it as unrecoverable and tells you to copy anything you need first.

That gives you the actual decision rule. Format once, correctly, in the camera. If the error clears, you're done. If the identical error returns immediately, on a card you've confirmed is unlocked and was just correctly formatted, stop formatting it. Put a different, known-good card in the same slot next — that single test tells you whether the problem is the card or the camera.

Card families: why formatting isn't one instruction

The SD Association defines four capacity families, and the file system a valid format uses depends on which one is in your hand:

This capacity-to-file-system mapping is part of why the SD Association recommends a formatter built specifically for SD-family cards rather than a general-purpose desktop format dialog: its stated reason is that operating-system formatting tools aren't optimized for SD, SDHC, SDXC or SDUC cards and can mean lower performance.

Traps worth knowing about

• A quick format is not a lighter version of the same fix. Where a camera offers the choice at all — check the table above for your own line — quick format leaves the old file data physically in place and only clears the index. It's faster, but wrong if you're erasing a card before handing it to someone else. Full format is the one that overwrites the data area.
• Formatting also removes protected or locked images, not only the ones you'd normally delete first. Both Sony's and Fujifilm's own manuals say this explicitly.
• If you're replacing the card rather than continuing to fight the old one, match the capacity family, bus and speed rating your camera's manual actually specifies — see memory card speed marks — rather than assuming any SD-family card will do.
• If the actual question is slot type, not capacity — your camera takes CFexpress rather than SD — the two physical formats are not interchangeable; see CFexpress Type A vs. Type B.

What to check on your own equipment

1. Pull the card and look at its edge for the write-protect tab. If it's down, slide it up and retry before doing anything else.
2. Read the label for the capacity family — SD, SDHC, SDXC or SDUC — and the capacity itself. That tells you which file system the card should carry.
3. Format in the camera, in the menu specific to your exact model — search your camera's current online manual for "format" rather than relying on memory, since the steps can change between firmware versions.
4. If your camera offers separate quick and full options, use full when you actually want the data gone, not just hidden from the file system.
5. If the identical error reappears immediately after a clean, correct format, stop. Confirm it's the card by trying a second, known-good card in the same slot, then replace it — see memory card speed marks for what to match when you buy.

Check it on your own equipment

These take you to the manufacturers and standards bodies the page draws on, so you can look up your exact model.

• Standards reference
  Download the SD Memory Card Formatter (opens in a new tab)The SD Association's free formatter for Windows and Mac, with a statement that OS-provided formatting tools may not be optimized for SD/SDHC/SDXC/SDUC cards, and that this tool complies with the SD File System Specification. — www.sdcard.org
• Official support page
  Canon: "Card's write protect switch is set to lock" (opens in a new tab)Canon's own explanation of the write-protect switch message and how to clear it by sliding the switch on the card. — my.canon
• Official support page
  Nikon Z6III manual: Format Memory Card (opens in a new tab)Nikon's own formatting steps for this body, including the quick-format/full-format choice offered only for CFexpress cards, not SD. — onlinemanual.nikonimglib.com
• Official support page
  Sony Help Guide: Format (α7 IV) (opens in a new tab)Sony's own explanation of quick vs. full format for this body's SD card slots, and how to trigger full formatting. — helpguide.sony.net