When an SD card displays "error", is no longer detected or asks to be formatted, you should stop taking photos or filming with it, and not format it: your photos and videos are almost always still present in the card's memory chip, and it is each new shot that risks overwriting them. Start with the mundane causes (the small protection latch on the side, another reader), then set the card aside and have it analysed if the problem persists.

What follows reviews the most common causes, what each error message means, and how recovery works, including on the tiny microSD cards used in drones and GoPro cameras.

Start with the mundane causes

Before imagining the worst, two minutes of checks often avoid a false alarm.

On a full-size SD card, look at the small switch on the left side: it is the write-protection latch. If it is pushed down, in the "Lock" position, the device can no longer write anything and often displays a protected-card or error message. Sometimes it is enough to slide it back up for everything to return to normal. This latch can also slip on its own in a pocket or a bag.

Next, test the card in another reader or another device, and gently wipe the gold contacts if they are dirty (with a dry cloth, never a cleaning product). If the card reappears elsewhere, the problem came from the reader, not from the card.

If none of these checks changes anything, do not persist. Remove the card, stop using it, and read on: the fault is probably deeper, and a wrong move at this stage can cost you your files.

What is inside an SD card

A memory card is a small miniature computer. Inside it are one or more memory chips, known as NAND, which actually contain your images, and a controller that orchestrates the exchanges: it translates what the device asks for and fetches the data from memory. The device never speaks directly to the chip; it always goes through the controller. This is why a card can appear dead while your photos remain intact in memory: sometimes it is only the access path that is cut off.

The format changes almost everything for recovery. A few years ago, cards were still opened where each component could be seen, the controller on one side, the memory chip on the other. That has become rare. Today, the vast majority of cards, and all the microSD cards fitted in drones, GoPro cameras, dashcams and smartphones, are monoliths: the memory chip and the controller are fused together in a single block of resin, with no component that can be isolated. This miniaturisation, now the norm, has a downside: it makes access to the data far more delicate in the event of a fault, because you can no longer simply desolder a chip to read it.

Your error messages, and what they mean

Cameras, camcorders and drones each have their own vocabulary, but the messages come back to the same small number of causes.

Message or symptom	Probable cause
"Card protected" / writing impossible	Protection latch on Lock
"Card error" / "card not initialised"	Corrupted allocation table, controller in difficulty
"No card" although it is inserted	Dead controller, dirty contacts, cracked card
False capacity or "card full" wrongly	Memory read fault, or counterfeit card
Missing thumbnails, last video unreadable	Corrupted files, interrupted recording

The reassuring point: as long as the card displays its true capacity and only a few files are problematic, you are most often dealing with logical corruption, the most favourable to recover. Conversely, a card that is completely invisible or announces an aberrant size betrays a hardware fault, which is a matter for the laboratory.

The cut-off video, and the wear of heavily used cards

Two situations specific to photo and video deserve a particular mention.

The first is the interrupted video. When a GoPro shuts down for lack of battery in mid-shoot, or the card is removed from a device still recording, the last video file remains incomplete: it is missing the final part that tells the player how to read it, and it then appears corrupted or unreadable. Good news, this type of file can often be reconstructed in the laboratory, by repairing its internal structure to make it readable again.

The second is wear. A dashcam, a surveillance camera or a drone write to their card continuously, for hours on end, in a loop. This is an intense demand that not all cards withstand. A cheap consumer card placed in a dashcam wears out quickly and eventually becomes unstable. For these uses, it is better to choose cards designed for endurance, intended precisely to absorb enormous volumes of writing.

Beware of counterfeit cards

There is a trap specific to memory cards, and it does a great deal of damage: false capacity. Cards are sold, often at knock-down prices on online marketplaces, as 512 GB or 1 TB, when in reality they contain only 32 or 64 GB of memory. The card's firmware is tampered with to announce a capacity it does not have.

The result is insidious: everything seems to go well at first, then, once the true capacity is exceeded, the new data is lost or overwrites the first. You discover the problem on the day you want to look back at photos that have disappeared or are corrupted. The remedy is simple: buy your cards from recognised brands and reliable resellers, be wary of enormous capacities at a derisory price, and test a new card before entrusting it with irreplaceable memories.

What a laboratory really does

When the fault is hardware-related, recovering a memory card requires the same know-how as recovering a USB stick, with the added difficulty of miniaturisation.

If the memory chip is unstable, we stabilise it, adjusting its temperature if necessary, long enough to extract its content. On the rare cards with separate components whose controller is dead, we desolder the memory chip to read it directly, an operation called chip-off. But the most common case today is the monolith, where nothing desolders: we then remove layers of protection to reach the test contact points left by the manufacturer, then read the memory through them with dedicated equipment.

But reading the memory is only the first step. The controller does not store the images there as they are: it applies several transformations to spread wear across the chip. The raw content that is recovered must therefore be reconstituted by applying, in the right order, the inverse algorithms, with successive error corrections until coherent files are recovered. Only then do the photos and videos reappear, to which usable names are restored if necessary. This work is long and highly specialised, and no consumer software can carry it out when the controller no longer responds, for want of access to the memory.

The right moves

Faced with a failing card, the essentials come down to a few reflexes.

✅ To do	❌ To avoid
Stop taking photos or filming immediately	Continue taking photos or videos
Check the protection latch	Format in the device or on the computer
Test in another reader	Force a cracked card into the slot
Set the card aside and have it analysed	Clean the contacts with a cleaning product

The decisive move is to stop using the card at the first sign of a problem. On a card of photos or videos, each additional shutter release can write over the files you hope to recover. And if your device or your computer offers to format the card, refuse until you have recovered what matters: the files are still present, formatting would only make them harder to find.

An SD card is not a backup

Like a USB stick, a memory card is made to capture and transport, not to preserve for the long term. It lives in devices that demand a lot from it, heat it, discharge it and recharge it, and it can fail without warning, often at the worst moment. Get into the habit of regularly offloading your photos and videos onto another medium, ideally several. A card should never be the only place where images you care about live.

Frequently asked questions

Why does my SD card display "error" or is it no longer read?

The causes range from the simple protection latch in the Lock position to a corrupted allocation table, a failing controller, dirty contacts or a counterfeit card. In the majority of cases, the photos and videos remain present in the memory chip; it is access to that data that has failed.

Should you format an SD card that the device no longer reads?

No, not if it contains important photos or videos. The device offers to format because it no longer understands the card's structure, but the files are still there. Formatting would complicate recovery. Remove the card and stop using it.

Can you recover the photos from a corrupted SD card or a dead microSD?

Often, yes. In the laboratory, the memory chip is read directly, by chip-off on a card that allows it or via the factory test points on a monolithic microSD, then the files are reconstructed by algorithms. Interrupted videos can also be repaired.

How do you recover a GoPro or drone video cut off in mid-recording?

When the device shuts down during shooting, the last video file is incomplete and becomes unreadable because it is missing its final part. A laboratory can often reconstruct this file by repairing its internal structure. You must not film with the card in the meantime.

How do you recognise a counterfeit SD card?

A counterfeit card announces a capacity far greater than its real memory (for example 512 GB for 32 GB real). Everything is fine until the true capacity is exceeded, then the data is lost or overwritten. Buy recognised brands from reliable resellers and test a new card before use.

Can an SD card serve as a backup?

No. An SD card is for capturing and transporting images, not for preserving them for the long term: it is a fragile, heavily used medium that can fail without warning. Regularly offload your photos and videos onto at least one other medium.