My EOS 550D is auto formatting my card

[Potatoo]

last month when I was in the middle of a shoot I got the error message “Card cannot be accessed. Reinsert/change the card or format card with camera.” After seeing that message turned off my camera and turned it back on, and it seemed like it solved the I error. But when I tried to look through all the photos on my computer after the shoot all the photos before the error was gone. I used recovery software and found out that all the photos had been automatically deleted. I don’t think cameras can auto format your card without any instructions from the user. 

I changed my sd card to a new one to make sure that it wasn’t my card corrupting. Today in the middle of my shoot the same error popped up again and when I tried to look for the image it was all gone again. It shouldn’t be my sd card problem since I got it last month and barely even use it.

I haven’t tried to recover the date on it but I’ll try later. Is there any mechanical malfunction that can cause this?

[BurnUnit]

The best place to start is to ask the exact brand, model and capacity of the memory cards you're using. Were they purchased locally or from an online vendor like Amazon? Are they full size SD cards or micro SD cards that require an adapter? Adapted micro SD cards don't always play nice in cameras.

[Tronhard]

Hi and welcome to the forum:
As my colleague referred to, using Micro SD-cards that use an adapter are not a good idea.  Furthermore, you should use respected card brands like SanDisk, Lexar and from reputable dealers like B&H.  There are a lot of counterfeit cards out there.
It is also a wise idea to format any card you get using the format command of the camera to make sure it is fully compatible for writing.  Cards are not autoformatted by the camera.

[normadel]

No, your camera (or any camera) should not be formatting the memory card by itself.  If yours is, there is an electrical problem with it. I wouldn't trust it at all. 

Your camera is probably toast. Fourteen-year-old model, no warranty. Canon won't fix it. 

[Tronhard]

I suspect our OP is jumping to the conclusion that the camera is auto-formatting his card.  That seems incredibly unlikely.  What I am more inclined to suspect is that he is using a bad card or cards: perhaps a micro SD card, which if it has movement within the adapter could cause that.  Or got cheap knock-offs and is suffering the consequences.
Waiting to see what they have to say about that...